I don't understand posters saying that the OP has pressured her mother into paying for an expensive ceremony she couldn't afford, and therefore it's only fair the mother takes all the money?
That's a huge amount of extrapolation going on!
Likewise the suggestions that the mother hadn't kept the money to repay herself (as the OP clearly said the mother told her), but have somehow moved onto a scenario where the mother is saving the money for her child to have at some point in the future?
I dont see the indications that any of this is happening? Even if the OP is very young.
"... the guests and her friends and she paid and we don't get to keep them because she's paid a lot and the grooms family didn't contribute"
I do wonder if there's anything behind the grooms family not contributing though? Were they expected to? Did they promise money? Or cultural tradition suggests they should have?
Altogether I think it depends on the wedding culture. If it's tradition for the guests to give money specifically to contribute to the wedding, and nothing had been said to indicate otherwise, then I get why this has happened.
It also depends on the guests, if they are from the same culture and expect their gifts and money to go to the brides mother, then there is no theft, as the money is being used as intended. If they gave specifically to you & your husband, then I do think it's theft.
Therefore I'd be writing a thank you note to guests that explains their money has not gone to you.
Whatever happens, the legal ceremony will now be rather awkward.
Good luck OP.