My mother used to tell me "don't ask questions if you don't want to know the answers" and that seems to apply well in this case. You have to consider that not everyone is raised the same way. Some people live in a home where there parents would walk around half or wholly nude in front of the children, while other kids, never saw their parents except when fully dressed. Some parents are very lenient about alcohol or drugs, while others would put their kids in military school for it. She is not you, so it's unfair of you to expect her to be like you. I give her credit, that she was honest and upfront about it and didn't feel the need to lie to you, which she could have easily done.
What has happened has happened...and out of those people, she chose to be with you. She chose to be upfront and honest with you about her past, and now you're sitting in judgment of her. Do you think that's fair? Would you rather be with someone who claimed they were so virtuous, while all the time it wasn't true. I think when you're with someone you have to make choices....you make choices about what's important and what's not important, based on your relationship with that person.
You can be upset with this and potentially ruin the best relationship of your life, or you can figure out how to put it out of your head and move on, it's your choice.
I welcome your thoughts, let me know if you want to talk more