Depends on the situation for the little girl, though.
Think this (which would often be the case):
She's in her house in her bedroom and a guy breaks in. He goes after her. She could, with self-defence training, hold her attacker off long enough to cause him to flee (since he's getting nowhere fast enough and her screams {which she might manage to do} are probably being heard by her parents). The guy's gonna realize he's gotta leave.
The same could be true in a public park, for example. If the little girl could fight off the adult long enough to scream and also make it a little tougher and longer than her attacker thought, he's probably gonna leave and the girl's fine.
Now, one-on-one with nobody around or if he manages to do something violent at the start (which, really, he probably could if he tried), then the girl really doesn't stand a chance.
But, often, the little kids (not just girls) could stand chances with some good training. And, as the example of the 9 year-old in this thread suggests, it is possible.