I don't know if this is an obsession or not (would have posted in Obsessions and OCD if I was sure)...:
For as long as I can remember, my mom has always obsessed over money...not actual cash, but money she has spent, mostly on others. Perhaps I nitpick, but this is one of her exceedingly rude and annoying traits. For example:
She cannot remember what day or month my birthday is, but she can remember the exact price she paid for a gift that I would have "died without".
She refused to let me give some teddy bears to the local thrift store (I am not into frilly cutesy stuff, but the toys are still very pretty and in perfect condition) that she had bought for me because she spent far too much money on them. And when I tried to neatly tuck them back in their boxes and put them in the safety of the closet, she took them out and put them in my room and then burned the boxes.
She got angry at me for wanting to give all my clothes that were too big to the thrift store because she spent too much money on them all (even though some of these shirts went low enough to show the skin below my bra! O.o).
I told her last year that I wanted nothing for Christmas and she went and got me stuff I did not want, but I still thanked her. I tucked it all into my empty dresser drawers and she yelled at me, saying how much she spent on each item, and them took everything back out and put it back under the tree.
And then if she sees something she bought for someone else being "abused", she always says "That's nice...I spent $xx for that (insert item)", or something similar.
It sounds like a serious psychological problem to me. Especially if she can't remember what month your birthday is in. Normal people don't act this way, even if they grew up in poverty or during the Great Depression. She needs help, but I wonder if she knows it. She may think it's the rest of the world who has the problem.
Her boundaries are blurred and she is taking the fact that YOUR teddybears/clothes..etc are still about her. If you remove them/give them away..etc, she's being rejected.
Somewhat narccisistic and self-centred, controlling and even obssessive.
My mom used to give people things that I gave her. (but I always felt rejected by my mom....the things became an extended part of me).
I've dealt with it through therapy. and your mom's issues are definitely beyond your ability to fix. If you don't take it all personally (almost impossible), and explain to her that if she's distressed over things that people have grown out of then she maybe should consider to spend less money.
Maybe you both could consider family therapy. It might be in your best interests considering her behaviour has already had much impact on you.
Best to you,
It's all a matter of perspective!