BJJ is a fine art to train in. Depending on the school, there may be more of a focus on the ground, compared to ground and stand up, but either way, you'll learn some fantastic ground work, and it gives an awesome cardio workout.
As for girls training in it...I think its a great idea for girls to train in BJJ. If a female is going to get attacked, there is a good chance she could find herself on the ground. BJJ will provide some great escape methods.
I've rolled with some females in class before, and many of them do a fantstic job. Actually there are a few that seem to do better than the guys, aggression wise.
I'd give it a try. Take a class and see what you think.
Mike