I need this job, I need this job, I need this job – Ursa repeats this to herself, in her head through-out the final interview process and it helps her keep her mask of polite submission firmly in place. Being submissive is made easier because Poppy Bei Fong has no real harm in her. Though Ursa finds her to be a woman of weak constitution and character, she does not seem at all vicious. Poppy's worst fault is that she seems so naïve. Even after years of marriage – she is not bitter and speaks fondly of her husband. It is the oddest thing Ursa has ever seen – and she has seen a two headed Koalasheep.
The Bei Fongs are in desperate need of a nanny. The last three nannies all quit in an untimely fashion – because they were unsuitable, according to Poppy. Ursa needs a place to hide and a job to support herself. It's just for now, she tells herself. Until she can figure out her next move.
Ursa doesn't need to be a servant. She has other skills. These skills, however, are not, strictly speaking, legal. But she is good at them. A little too good she sometimes thinks. A few carefully chosen ingredients, ground up and then a sudden massive stroke that looked completely natural. Her hand didn't shake in the slightest when she added that delicate powder to the old man's tea. She hadn't hesitated at all – and this lack of hesitation bothers her now. Ursa did not want to think of herself as a ruthless person.
She could make much more money, using those skills. But Ursa did not think it was worth it in the end. As soon as you started thinking it was easy, you forgot what it really cost. So Ursa was going to be a nanny instead. A common household servant. One of thousands of common household servants. She will get the anonymity she has been searching for here.
This will do nicely. Largish, but relatively insignificant town. A live-in position. Easy work... after all, how much trouble can one sickly, six-year-old girl be? Ursa has not yet met Toph, but Poppy has assured her that her daughter is mild mannered and well behaved. Ursa would not mind how she behaved, not really. A small selfish part of Ursa just wants to hold a child in her arms again and to be needed. She misses the way childred need - simply and with meaning.
Even if it is all pretend, it might make the clenched knots in her stomach loosen. Ursa's stomach feels like it is in so many knots that she'll never be full again. She can taste how much she misses her children.
She can feel their absence in her very bones.
Small notes: I also subscribe to the Ursa = master poisoner theory.