Help! My mother just might be a thief?

My mother visited me in my aunt's house, and she wanted to go out one day right? I asked her if I could bring my Christmas money so I could buy an Amazon card. She asked me how much I had. I told her. $215. She said no. So I put it back in my room. So I come back from a basketball game and sleep. I wake up, and talk to my mom. During the conversation she mentions that she took my money. So this means she went INTO MY ROOM, WHILE I WAS SLEEPING, and TOOK MY CHRISTMAS CASH. Now I keep asking her for the cash back, or the credit card she promised. She kept saying "tomorrow, tomorrow" so many times. Until today. I got late Christmas money from my uncle, and my mom says that since I got money from my uncle she will only give 100 dollars back to me. It might not seem like a big deal, but I'm young and money is hard to come by. So I say she should give the full 215 dollars back, but she says, no no no so I'm so shocked. She has plenty of money already! She doesn't need to take and keep couple hundred bucks from her son...

I wanted to buy a more modern phone, I had this iPhone 4 for a while, and now finally I have the money to upgrade. But she says, no this phone is fine.

And bear with me, but just now she says she will NOT GIVE THE MONEY BACK.

Is this fair?
Is this even legal?
But maybe it's just me and I should have never shown my cash to my mom in the first place.
I don't want to seem greedy, but that was my money and she took it.

Please advise and thank you for reading.