Well, there is a perception that most guys want to date "bi" girls so that they can watch or participate. The plain fact is, though most guys won't admit it, most guys don't want the girl that they are in love with to be doing anyone else. Most guys that do this do it with a girl that they really don't have strong feelings for.
First off, you aren't even sure she has dated girls in the past at this point, so to write her off on a suspicion would be bad. What you should do is just treat it like any other relationship. You may not hit it off at all anyway, and it may be a non-issue. If you do hit it off, then come about the topic when it appears.
So, on the whole, I wouldn't be concerned about it.