I'm sure that in that case you would make it clear the money was a contribution towards the house purchase. OP's mum seems to have given her the money randomly then only recently (after it was spent) specified what it was supposed to be for.
Yeah, the mother should have said what she wanted the money spent on before she handed it over. If it was just a random gift, then it's fair game on what the money is spent on.
I'm still in shock about 8,000 on games. But, the mother knows her daughter, and if she's an adult being stupid with money wouldn't be a surprise at this point.
Personally, I would not give DD this amount of money unless I knew she would sensible with it. If she needed a bill paid, I would call the company and pay it, not give her the money flat out.
But this still seems to lack maturity. When I was 16 my father gave me about $300 for spending money on a trip. I spent all of it on trips to movies, nights out, etc.. When I got back my father asked for the change, while I stared at him blankly. He got upset I spend all of it, when he never told me not to. I just asked him why he gave me $300 if he didn't want me to spend it. You have the maturity of a 16 year old, OP.
That should be a life lesson to anyone giving someone money. They will spend it differently than you envisioned unless you tell them the conditions of the gift.
Be honest with your mother OP, that way she knows what her money is going towards. Not telling her because you know she might stop giving you money is deceptive.