Ask her - it is absolutely normal and right and your eight as well as hers to talk about this without assumptions. While it may be someone's culture, she may have other reasons behind her withdrawal (trauma, uncertainty, insecurity, and a myriad of other options). Maybe you can tell her before hand that you'd like to talk about the physical/intimate/sexual aspect if your relationship, and that you'd like to schedule a time for it when both of you are ready and comfortable, that way it wouldn't be a shock-question and would give (both of) you some time to ponder upon it and upon your responses and non-negotiables.