We think we found her... help?

Send her a message through Facebook, and ask her if your fiance's date of birth holds a special meaning for her. Tell her that you think she may be a special person you've been looking for. You may want to send a friend request at the same time because FB usually puts messages from non-friends into the "Other" message folder, and people usually don't check it. (In fact, I told my brother this just the other day, and when he checked his "Other" folder, he found literally hundreds of unread messages from the past couple years.)