I don't think you're wrong for feeling self-conscious about this.
But also, I don't think the fact that she's had such a past means she should have to stop contact with all her exes - if it really was casual sex especially.

I think it all has to do not with her, but with YOUR values, and also about the RELATIONSHIP between the two of you. Is the relationship secure and solid? Sometimes, feelings of jealousy can happen because something isn't happening in the relationship. I went through a situation where I thought I was jealous of my ex's ex and it was my fault... looking back I can see that there were severe relationship issues and he was not being faithful in ways NOT related to that ex. Somehow those insecurities transfered onto the ex's ex, and I got insanely jealous. In my case, he still was not "over her", even though he claimed to be. She had been his only partner previous to our relationship.

our situations are different - I just wanted to say it can be very complicated and I think the more true to yourself and your relationship wtih this person you can be, the better results you will have.