As someone who, in the past, has actively pursued someone in a relationship, ended up with the person eventually, only to have this person "stolen" (for lack of a better term) from me in the same manner, I would totally advise against going after her. About the time someone does the same in return, you'll be shattered and you don't deserve that.

Scorpiosis' advice is solid. If it's going to happen, let it happen naturally.