RORY: Just for the record, I’m a girl and we are supposed to throw like this. [throws the ball]
“You throw like a girl” is an insult given to someone, usually male, who throws a ball or object in a manner which is judged to be feeble or incompetent. “The girlie throw” is one which uses the space around the thrower in a restricted manner, with only the hand and forearm being utilised in the movement.
Rory is taking ownership of “throwing like a girl”, and not seeing it as a flaw that needs to be changed or fixed about herself. And in fact, she is successful at the bottle toss game, unlike Jess.