Yes, she should have told you before any sexual contact, when your clothes were still. Some people forget that oral sex is a form of sexual contact (duh). Also, these days many people have genital herpes in their mouth and it can be spread through oral sex that way. (If the person only has it genitally they cannot spread it through oral sex, so you may not have been put at risk.)
If you are afraid that you have been exposed, you can get a blood test for STD's and make sure they run the full spectrum and check for herpes as well. It can take from 1 to 2 weeks from the first exposure until the first outbreak, so I would wait until it has been at least 2 weeks from your initial exposure before having the blood test done.
If you decide to keep seeing her, just make sure you wear a condom every time and if you wish, take a quick 2 minute shower after sex to wash her fluids off of you. I hear it reduces the risk of exposure, although I'm not sure how much. It is a virus and like washing your hands, washing your body reduces the chance of spread. There are also prescription medications that can suppress the virus in her body and reduce the chance of her passing it on.
I don't think her having herpes should be enough for you to not want to see her anymore, however.... not telling you that she has it before sexual conduct does give me a cause for concern.