Yes, it is possible to contract oral herpes from genital herpes and vice versa. (They are two different strains but both can cause genital herpes. Only one can cause cold sores.) However, I think the chance of spreading it when there is no breakout is much less than there is when an outbreak is present. Keep in mind that you are much more likely to spread it a few days before or after a breakout as well. (If she has any tingling sensation around her mouth, that is a pretty good indication that she will soon have an outbreak.)