I'm so sorry to hear what happened with your sister. It sucks that she wouldn't drop in and feed your kitty but she does have the right to say "no."

I understand that you resented her not spending Thanksgiving with you and your Mom after your dad died. Everyone grieves differently, though, and throwing it in her face a year later in response to a separate matter is not ideal. But of course it's the anniversary of his death.

Her insult to you may feel very personal but it sounds to me like she was lashing out after being told she was not part of the family, which is already a sore spot with her.

Sounds like things escalated quickly due to built-up feelings. I hope you two can reconcile. It really sounds to me like you both got triggered. Disowning her is unwarranted in my view. Sisters say things like that to each other - I've heard it before. You can get past this.