I don't want to see people keep questioning her motivations for buying goods. In my point of view, that was her money and she could do whatever she wants to do. Let's back to the point, I was not so happy to let her control my financial resources, and that is why I posted this discussion to public and sought for suggestions.
I am glad someone did give me some very thoughtful suggestions for a direction. But some others... I am sorry, but I am not here for your criticism. I appreciate all helpful shared experiences and suggestions. And I have taken all of them and have my own approaches generated already. Thank you all.
Anything else more than suggestions, sorry, I can't take them as I don't think that makes any good to me, to my girlfriend, or to my relationship.
My girlfriend, she might not be the perfect one in the world, she might want to buy some fancy big brand purses sometimes, she might want to buy some costly customer electronics for herself. But that all her money.
I have chosen my way to deal with it after so many suggestions. And I am not stupid, I will also have my firewall established for myself. Thanks for all given suggestions. Thank you.