It all depends on your mindset. I agree with what the others have said, but i understand where you're coming from. Personally i'd be in the same predicament if my situation was similiar, as it would bother me. I couldn't even explain why, it just would.
If you are really keen on this girl then work hard to get rid of those thoughts and get over it, whatever you do, do not throw it in her face if you two argue. Her past has nothing to do with you and it is very hurtful and disrepectful to bring it up.
"Never make someone your priority, when to them you are only an option"