I think since she's not a close relative or someone you need to have an authentic connection with, it's probably not worth investing much in trying either to get on with her or set her straight. I'd be inclined to keep it polite but just try to engage as little as possible, or if she directly interferes, assert yourself without criticising or becoming angry.
If she contradicts something you've told the kids, say 'Oh, we normally do it this way in our family', then reiterate what you said in the first place.
If she complains about something, 'It's a shame you don't like it'.
If she disapproves of presents, just ignore and say thank you as normal.
If she says something generally disagreeable, make a neutral reply ('I see' or 'I hadn't thought of it like that' or 'Well I know there are different opinions about that'), then change the subject.
If she attacks you personally, don't take it but don't retaliate: 'Don't speak to me that way please' - then leave the situation.
Remind your husband before you go how awful she is, so he can look out for you again.
If she gets too much, take time out to go to the loo, check on the bird, text a friend etc and get some deep breaths.
If you find yourself alone with her, wrap her up in foil and stick her in the oven for 15mins per lb.
Hope this year is nicer!