Well, without being rude about it... Accept the fact that people help out those they are close to, and don't be quite so unaccepting of her attempts to make your (hopefully still) upcoming partnership a reality. Consider what you would do if the situation were reversed...I expect you'd do your best to help her through a temporary tight spot. I'd suggest you tell her that you need to get used to the idea of sharing, and that you want an opportunity to do so.
I've been married for 33+ years, and retired about 2 years ago. Herself is still working, and it has taken a lot for us both (especially me) to get used to the idea that she is now the principle earner, and its really ok if I don't pay for everything. It is probably even harder (and I can't remember back that far) if you've been used to being independent and now will be part of a couple.