You could try displacement. Every time you think a thought about her, replace it with something else, ideally a positive memory about something else you love / do / have achieved.
Its a case of tricking your mind. Pretend the situation is different. It works in a similar way to the "fake it till you make it" method does. Ie. You convince yourself of the new thoughts. Eventually, you won't even have thoughts about her.
I'm not an expert, and its my own theory, however, this is what worked for me.