it sounds as if you mom might be financially strapped and wants you to have a nice wedding, but can only afford so much.
be honest with her and ask if it is a question of money...if it is, try to be flexible...i know you think what you eat, how fancy the place is, etc., is soooo important. in the scheme of things, it isn't. you can have a lovely wedding if you are reasonable and do what you can afford.