Set just before the end of Doomsday, before the Doctor contacts Rose and they meet at Bad Wolf Bay.
"Mum, I know what I saw!"
"Sweetheart, you 'see' it every bloody day! I know you miss him and I know you love him, but I'm startin' to worry 'bout you!" Jackie's brow creased as she regarded her daughter. Rose's face was beginning to become red and her eyes were frantic as she stood and began to pace around the room.
"Stop it! Stop talkin' to me in that voice! I'm not crazy! I'm not just seein' things because I want them to be there. It was there, Mum. The TARDIS, she was there! "
"Rose, you've been here for two months. The rift is closed – the Doctor's not comin' for you."
"He is!" Rose shouted frantically. "He – he has to be!" She tugged at her hair in frustration. "After everything we've been through, he can't just give up on me! He'll find a way through!"
"He said it's impossible," Jackie said softly.
"He's been wrong before!" Rose screamed, turning on Jackie with wild eyes. Jackie flinched away from the pain she saw in her daughter's eyes. "He said travelling between parallel worlds was impossible and look where we are now, Mum! Look at us! We're proof that it's not impossible! I'm not givin' up! I'll even get a job at Torchwood if it'll help! I'll find a way back to him if it's the last thing I do!"
Rose stormed out of the room, leaving Jackie behind. The older woman sighed, sinking down into a chair and leaning her head against the kitchen table. "I'm so scared that it will be the last thing you do, Rose. So scared."
Jackie understood that Rose was having a difficult time adjusting to a normal life without the Doctor. She understood that Rose was heartbroken because she loved the Doctor and would probably never see him again. She understood that Rose had been able to go anywhere, anywhen and that she had developed a wanderlust that could never be fully sated. She understood that she simply wasn't enough anymore for Rose.
But what she couldn't understand was why Rose preferred illusions to reality. She knew it hurt Rose each night when the dreams came, dreams of the Doctor (although Rose would never go into greater detail than that), but Rose still craved those dreams. She knew that Rose saw the TARDIS around every street corner, the Doctor in every dark haired man with a pinstriped suit, but Rose would do nothing to convince herself that those were just her imagination.
Going back to reality always hurt. So why did Rose do nothing to stop the illusions?
Jackie hadn't fully understood Rose even before she met the Doctor. But after the Doctor came, swept her off her feet and took her off through time and space, Rose had changed. She'd matured and seen things that no human should ever see. She'd saved the Earth a few times, and the universe probably a couple more (as far as Jackie knew). She'd met the love of her life, an alien who didn't even have a proper name.
But Rose was human and she was young. She'd move on eventually – she had to. She couldn't go on living like that, listening every moment for the whirr of the TARDIS, looking out for the blue box everywhere she went, hoping to see a familiar alien with gravity-defying hair and brown suit whenever they went out. No one could live like that. Always hoping, always being disappointed.
Jackie had to believe that Rose would move on. She couldn't imagine watching Rose live like that, day after day. She had to believe that Rose would fall in love with someone else, or at least would learn to be content with her life. She couldn't even contemplate the possibility that Rose wouldn't move on, the possibility that Rose would pine after the Doctor for the rest of her life. Rose would move on, she believed. It was only a matter of time.
But Rose wasn't the only one who suffered from illusions. They both did.
Rose believed the Doctor would be able to come back and take her with him throughout time and space once again. She believed that he'd be there again, holding her hand and whispering "Run," if only she waited long enough.
Jackie believed that Rose would eventually move on from the Doctor. She believed that Rose would eventually find someone – hopefully a human being, although Jackie would settle for an alien if he made Rose happy – who would help her to heal and forget about the Doctor.
Both of them wished their illusions were reality and both of them hurt even more when it wasn't.
Going back to reality hurt, but illusions were all they had left.