As someone who's been in Ilya's niece's position, in fact I still am; one thing I'm certain about is that she'd hate Ilya's guts. There's so much complication that comes with knowing that your rich and capable uncle just isn't here, as your grandfather wastes away, as your father bears the brunt of it. It's ridiculously easy to forget the sins of a sick man. It's not that clear-cut and dry, but more often than not it feels like it. It's easier to think in black and white, to villainize your uncle for trying to lighten a mood that you've been suffocating under the weight of for years, when all he does is dip in every once in a while, distinctly more American each time, takes a little bit of the load off before you're being crushed under it all over again. I imagine it's not much better with Alexei's likely berating of his brother, and the fact that Ilya's Niece is likely to be surrounded by this environment 24/7. She wouldn't be mad at Ilya for betraying her at all. It's more likely that she'd hate him blindly until she sits down and thinks about it, and it's less and less rational even in her own head, how she perceives him. Personally, I took to seeing my uncle as an outsider, regarded with ample mistrust and irritation. It wasn't fair, but it wasn't like he was going to be there very long at all for me to suffer the consequences. It would get even more annoying when he'd offer to take me with him, 'respite' cleverly twisted to sound like 'vacation'. Also, man, accepting any sort of gift felt like receiving charity. Even if your father is a piece of shit, in times like that it's easy to write it off as stress. I bore witness to several times my father deliberately held information back from his brother, definitely about their father's condition. I know that at those times I felt vindicated more than anything.
tl;dr, Ilya's niece and her uncle's dynamic would be fraught and complex. I've always thought that, if anything, if they ever met again outside of Russia, it'd be so she could throw the trust fund in his face. She wouldn't hate him for being queer (might be my own perception of reality marred by me projecting on her, and headcanoning her as queer herself), or for defecting, really, but I doubt she'd grow out of the mindset of the little girl who loved her dad watching as he crumbles under the pressure of taking care of his dying father while her uncle just isn't there-- except to throw money at them, of course.
