I guess it's because she's always seen herself as someone selfish and quite "evil". So, she doesn't have it in her to actually care for someone and all that, but that's just her image of herself you know. I guess the author made her that way so she could get some character growth from an evil, selfish one to someone who is starting to become less selfish and more caring.
Probably because before now she only thought of her as someone to use. It seem like the prince is changing her slowly and she's now becoming more than just someone who only think about revenge.
Probably.
Yeah, I guess so.
Why can't the female lead use Sasha yet still wish for her happiness? She can still sincerely hope the best for her while still taking advantage of her.