Don't focus on doing oral just to get her off, you're too focused on the end point and not enough on the fun ride in between. There's so many variables involved in situations like these. Do you give it often enough? Has she orgasmned before? How long are you willing to spend down there before you 'give up' because it's not working. (That kind of pressure is difficult for both parties, remember there's not alarm that's going to go off if she doesn't get off in 20 minutes right?) Communicate with here, that's incredibly important in your sex life. Don't stress!
