Yep, been there, done that, got the T shirt.
The best thing you can do is to not discuss your personal business with her. That way, she won't be able to dish out unsolicited advice. If she asks pointed questions that you can't ignore, give a vague answer. For example, if she asks how much you're paying for your house, answer "Too much" or something else noncommittal. If she asks about your continuing school, just say something like you'll manage. One important thing is that your fiance seems to side with you. That is very, very good.
If you keep refusing to get involved in a conversation that you don't want to have, she'll eventually quit butting in. It does, however, seem to take a long time so hunker down!
BTW, if all else fails, you should check out
http://www.motherinlawstories.com . Believe me, reading some of those stories will make you feel better about your future MIL!
GOOD LUCK!