This is JKR's world and characters. I am simply extrapolating.
Hogwarts Diary 1995
We arrived several hours before the train carrying the rest of the students. My mother was concerned that we meet with Headmaster Dumbledore before the Welcoming Feast. My transfer from Durmstrang was not one that the Headmaster had anticipated. He welcomed us cordially, then examined my OWL scores. He sent me off to see Professors McGonagall and Snape in the teachers' lounge. Mother wanted to extract some sort of promise from Dumbledore without me around, I know the way my mother manipulates men. Since the disappearance of my father, she has been frantic to get me away from our old life. My father is Igor Karkaroff. Mother is desperate to keep me safe from the Dark Lord. She fears if he finds out I exist, we will both be killed. I found both Professors sipping tea in the lounge. I handed Professor McGonagall my OWL scores, her eyes widened before she handed the letter to Professor Snape. He smiled serenely and handed the letter back to me.
He spoke then. "You received eight Outstandings and one Exceeds Expectations on your OWLs, well done, Miss Leonidas. Has the Headmaster decided which House to place you in yet?" He was looking at me as if he already knew me.
"He said Slytherin House would be best, something about hiding me in plain sight. You are perhaps already aware of my parentage, Professor?" He was very like my father, calculating, aristocratic, and aloof.
"I knew your father quite well once. Has there still been no word from him? With these scores you can achieve almost anything you wish as a career."
"I want to train as an Auror. I want to take the classes that will get me into that training. I want to fight the Dark Lord. I love my father even if he was a Death Eater. I am proud to be Igor Karkaroff's daughter."
Professor McGonagall nodded and assigned me to the classes best guaranteed to get me into the Auror program. She warned me to keep quiet about my family and not to trust anyone.
Professor Snape added his own comments." In addition, do not tell any of our Quidditch mad students that Viktor Krum is your cousin. I will be available for any questions or concerns you have. I will make time for you to work on Defence this year because we have a problem about the teacher for that class."
I found Professor McGonagall to be a conscientious woman. I liked her. Professor Snape was not as easy to read. I felt he was hiding something. However, I also felt he had been a friend of my father's and that he truly was sorry his friend had disappeared. I went back to the headmaster's office to find my mother ready to leave. She hugged and kissed me before leaving with tears in her eyes.
Headmaster Dumbledore escorted me to the Slytherin dormitory. I was assigned to a room of my own because I was a transfer student. I thanked the headmaster for that, and then unpacked my trunk. I decided to start this journal now to put down my impressions of my new life. The other students in Slytherin House are not what I had expected. These students are not here to learn but to ponce about acting arrogant, making life difficult for others. I am charming this journal so that only those I give permission to can read it.
21 September 1995.
I have seen exactly what Professor Snape referred to as a problem with the Defence Against The Dark Arts teacher. A more stupid cow I have yet to find. The woman is an abomination. She has taken her spite out on a poor Gryffindor boy. She is truly evil. How this person can work for the Ministry of Magic is inconceivable. She should be sent to Nurmengard, she would be a fit companion for Grindelwald.
I have found the best way to avoid the others in Slytherin. I have taken to speaking in French only. Most of them cannot speak the language so they leave me alone for the most part. I have found that the teachers except for the Umbridge cow all have taken up the deception at the instigation of Professor Snape. He is exceedingly odd in class. He tends to sneer at the less gifted students but he always has a 'Tres bien" for my potions. I have now been subtly taken under the wings of all the teachers. They have me assisting in the Library, grading First Years' papers in Charms, Transfiguration, Potions and Herbology. I am also assisting Professor Flitwick with cataloging supplies as well as assisting Madame Pomfrey in adding to the medicinal supplies. They are all trying to keep me so busy that I will not worry for my father. I appreciate what they are trying to do but I still dream of him.
I am waiting until next month when I become of age. I will try to find a way to assist the fight against the Dark Lord. My deception about language is working so well the arrogant little Malfoy prat no longer watches what he says around me. He must think if you do not speak the language, you must be deaf and stupid also. I have reported what tidbits he has let drop to the headmaster. He says that once I have achieved my majority he will allow me to attend a meeting of a group he hopes I will join.
I have weekly meeting with Professor Snape to make sure my Potions proficiency is up to his requirements. We have been brewing some of the harder potions, which will surely be included on my NEWTs. He talks to me of my father sometimes. I feel I am getting to see a side of Professor Snape that few, if any, see. He talks to me of my mother also. He knew her also, when she and my father were first together. I know Professor Snape is years younger than either of my parents so he must have been just a boy newly recruited in the ranks of the Death Eaters. I know my father tried to turn him in to the Wizengamot when they wanted names of Death Eaters, and that Headmaster Dumbledore vouched for Professor Snape.
I do not know what is going on with Professor Snape but he is not what he appears, of that, I am certain. He is as secretive as my father. I have only weeks to go until I am of age. I cannot wait. This year and next year are all the schooling I have left. I want to be fighting. I want my father back. I miss my family.
1 October 1995
Headmaster Dumbledore wanted me to stay at school instead of going on the Hogsmeade outing. He told me that I was to have a visitor. My cousin Viktor had come to bring me letters from my mother and presents for my birthday. He and I met outside at the Quiddich pitch. Professor Snape had escorted me to meet Viktor. They eyed each other warily. Then Snape turned to return to the school. Viktor asked me if I was having any problems with Snape. I told him truthfully that Snape was helping me adjust, that he had been very kind to me. Viktor laughed and said that it was probably only because I was brighter and more driven than the other Slytherins. Then he suggested that I befriend a younger girl in Gryffindor. Hermione Granger. Viktor said she was as smart as I was and almost as solitary.
"You both are very strong females. Your Professor Snape does not like her because she is Gryffindor but he cannot deny that she is brilliant. She would make a good friend for you, little Thera. She also speaks fluent French so you could keep up your charade. Forget for a while your determination to fight the Dark Lord. Find a nice boy to date. Be your age, none of us may live to be much older. I wish you happy on your birthday."
He gave me a quick hug and kissed my forehead before striding off to the apparition point just outside the school grounds. I walked back to the Hall to find Snape waiting for me. He merely turned to walk me back down to the dungeons. I asked him if I could speak to him privately. Nodding he led me into his office. He closed the door and cast a spell to muffle our voices. I asked him what he thought my chances were of getting into the Auror program. He answered me more truthfully than I had hoped. He said that it would be difficult, that my parentage would most likely work against me. I would be suspect, and I would have to work harder than other candidates to prove my worth. Then he asked me a question. "Are you completely serious about fighting him, Miss Leonidas? Dumbledore has it in his head to bring you into the Order of the Phoenix. He wants to make you into a spy for the Order. I am to teach you Legilimency and Occlumency and whatever dark magic you have not already learned at Durmstrang. In other words, he wants to have the two of us work together. The Dark Lord thinks I am loyal to him and him alone. I have worked very long and hard to keep him believing that. You must be very certain that you can do whatever is required of you if you want us both to survive this. I will speak to Dumbledore again about this before Wednesday, which is our next meeting. Say nothing. In addition, young Viktor is correct that you probably should try to make a friend of Miss Granger. He suggested it to me before you came out. You are both very intense young women but you are more focused, perhaps because you are the elder but she could benefit from the friendship as much as you would."
I told him I would consider it. I told him that my father had taught me both Legilimency and Occlumency as well as most of the Dark Magic he had known as a Death Eater. I had much to think over. I do not think the headmaster would be pleased that Snape had told me as much as he had. I would find out next week. They morning of the 3rd I would turn seventeen, be legally an adult. My mother had sent me a handful of the little blue glass eye trinkets that we Greeks say ward off the "evil eye". Viktor had left me a letter telling me of the flat my mother had acquired in Chelsea. It has three bedrooms and a sitting room/library. Only Mother, Viktor and I would have access, unless of course, we brought someone else in with us. He gave me the address and the spell words necessary to enter. I spent the rest of the day doing the assignments for next week. I thought that I would seek out the Granger girl. I would like to have a friend here at school.