Who says you're supposed to be upset?

If someone you dislike/hate dies, relief (and joy) are the natural byproducts.

A tyrant dies, people celebrate, this is normal. Why is it any different going from a crowd-scenario to an individual one?

Good call skipping the funeral, too.

My immediate family are saying things like "if you want to talk about it..?"

I don't. It's not that I'm pleased she's gone, either. I felt maybe a pang when I read the EMail from my dad (she was his mum, and he lives in Germany), but to me it's no loss. I'm only sorry she never realised (or was told) how despicably she behaved to me, and how it affected me, for which she never apologised - not even the bite.

As for the funeral, the only way I'd be able to get down there anyway is if I got a lift with my sister, and she's working. So, no funeral, no morbid depression, no pretending to give a monkeys to relatives I haven't seen in years, and even then had no clue as to who they were. 'Cos I don't feel anything much anyway, and I'd likely start shouting about how shitty she treated me, which is not what people want to hear at a funeral.

I say good call to you.