What does "girl bites dog" mean?
What exactly don't you understand?
The word bite means that you hurt someone/something.
Usually we bite into an apple (because we want to eat it - so we don't actually hurt it).
When a dog bites a human, the human gets hurt.
"Girl bites dog." simply means that the dog got hurt by a girl.
It's unusual yet not impossible.
In the series "Good luck Charlie" on Disney Channel every Satuday night, there's an episode called "Girl Bites Dog"!?