My mum was a sweetheart from menopause onwards. Made no secret of the fact that she'd hoped I was the menopause (the last of 6, so I can't really blame her for that one!). She never held my hand as a kid (my earliest memories are of her shaking my hand off and telling me not to 'hang on to her').
She told me that I'd never amount to anything and spent years knocking everything I achieved.
The best was when she told me that I'd probably gotten aids (thanks to my numerous boyfriends when I was in my twenties) and not to go near her grandchildren in case I gave it them! That was probably her finest moment.
But you know what? She's in her 80's now and she's chilled a bit and though we were at each others throats for years, she's still my mum and I still love her.
This is your mum. The possibility of mental illness is very real, as other posters have said. But if it's just nastiness, you have to find a way that you can deal with this. If that means avoiding her, do it. If it means forgiving her, then do that instead.
Personally, I'm really glad that I've been able to forgive my mum for a lot of the things she's done and said to me (too many to mention). Cos I look at her life now and I can empathise with her. She had a rough time in her life...no money, herds of kids, no life. She dealt with it the best way she could. She wasn't one of nature's earth mothers and isn't one of nature's little sunbeams. It takes all sorts.
And you've got to remember that your mum comes from a different generation and this is probably a new concept to her, mothering and working. I can't sympathise enough with how crap this will be making you feel and your mum was bang out of order for saying it, but if (God forbid) she died tomorrow, would you feel guilty for not extending the olive branch???