Sorry about the delay. I just got your question. Sexual pasts are a very difficult thing to discuss. There is often embarrassment or a feeling that one will be judged. She may be concerned about the way you will perceive her. If there isn't anything in her disclosure that changes the way you see her then I would let it go. There are multiple reasons why she may not have disclosed. Make an agreement for this point forward to not hide things from each other. Discuss her past openly so that you can begin to feel better about the past. If there is something significant like high risk behavior then resolve this between the two of you. Not everyone wants to maintain a relationship knowing deep dark secrets about the other person. Just make an agreement to be honest now. You have to decide what you will accept in terms of sexual histories.
If this has been helpful press accept