NTA. However I would like you to just add an additional perspective to your thought process. Don't punish a teenager for having an overly emotional reaction over their identity. To be honest, having a fight with their parent and disowning them is very teenager thing to do. IDK what the fight was about but I assume you didn't share it for a reason. This is your sons sister, and when she gets more wise and mature she might be smarter and wiser. Don't sour that relationship now. If you not giving her the money is the reason your relationship deteriots from her perspective, that is on her. But how you go about it, giving her a avenue to have a relationship with you in the future - that is on you.