Just let her talk about it as often as she feels the need and be understanding - don't rush her to get over it or let it irritate you when she talks about him (or the situation she finds herself in), and she will get over it in time. As you probably already know - teenagers don't really understand too well about time being a healer - everything has to be NOW. Also, try not to insist that its just a child hood fling, as these things are so important at 13.......and as a result of this, she will grow to trust her own feelings and thoughts thru' adolescence - like the Dorothy Holte piece -
If a child lives with criticism, he learns to condemn;
If a child lives with hostility, he learns to fight;
If a child lives with ridicule, he learns to be shy;
If a child lives with shame, he learns to feel guilty;
If a child lives with tolerance, he learns to be patient;
If a child lives with encouragement, he learns confidence;
If a child lives with praise, he learns to appreciate;
If a child lives with fairness, he learns justice;
If a child lives with security, he learns to have faith;
If a child lives with approval, he learns to like himself;
If a child lives with acceptance and friendship, he learns to
find love in the world.
Hope this helps.....