Am I wrong about this?

I am together with my girlfriend since almost 2 years. I really love her but I started to doubt on her a little. She never kept secrets from me before, I mean she told me every little detail whatever she did. But lately she keeps borrowing money from me and not telling me why. Just saying "It's about my family, they need the money because they didn't get paid this month yet". Honestly I do not believe that I would be able to help her family or that they would even need my help, and I am almost sure that it isn't about her family but she is using it for something else. It's not a really high sum, and I don't really care about the money, all I care is for her to tell the truth...I just want the reason. Few days ago I decided to open this subject to her (I know it's wrong to talk about lending her my money but I only care for the reason). However she misunderstands it yelling at me and saying "I'll give your ******* money back, you didn't really do me that much of a favour to always remind me of that etc". I just want to know what she is doing behind my back, I don't care about my money. Am I wrong?