If you care so much about what other people think of you talking to her, just kidnap her and and chain her up in a shed.
Then you sit down, and have the most wonderful talk to her about how much you love date rape and how much of a loving alpha you are.
Anyway, this is a rather double edged sword situation, one thing is that you're friends with both her and her ex, depending on how you make the move, one side can get the wrong idea, I'd suggest you try to figure out somehow if her ex still likes her, not being obvious about it of course.
But if you think it's safe to take the move, don't be afraid to talk to her more often, but be casual, you don't have to exagerate, just try to get closer to her so she can feel safer with you around, and when the moment is right, ask her out, women are not pandora boxes if you know how to play your cards in the right time.