If you've ever watched "Good Luck Chuck" with Dane Cook, you'll be able to grasp this idea pretty quickly...
In the movie, Chuck is said to be a "lucky charm" because every girl he sleeps with finds the love of their life straight after. It's a gift, but a curse.
And the same is happening with this girl. She has noticed a pattern... every time she gets close to getting serious with a guy, he mysteriously disappears and immediately gets a girlfriend right after.
So she starts to think... maybe she's the practice girl? Maybe guys practice their charm and witty ways on her, only to go use them on someone else?
Her disappointment turns when she discovers that, maybe, she's the girlfriend fairy, with a charm just like Chuck!
Watch this hilarious illustration of being a girlfriend fairy!