Putting on my therapists hat here: It sounds like you need to have a discussion with her on how much is OK. It is just a fact of life that she is going to want to donate. Better if she tells you how much so you can make compromises than if she sneaks around and gives even more.
Saying "I have told her she doesn't see any more of my money until she tells me what she is using her money for" sounds like something a controling person would say. That will never wake her up to TTATT. It will only make her did her heels in deeper.
And who knows maybe she is out buying you a big fat birtday present with the money.