Problems I find, besides the ones already mentioned, are stepping in the bucket and either swinging late or early.
hands back
With my girls it's pulling their heads...
Listening to mom or dad that are yelling "keep the elbow up" and "nice level swing."
My biggest gripe is in the 6-8yr old coach pitch leagues where the coaches pitch a ball to the girls that looks like something you would see in church league softball. To me, this is why you see so many little girls with there back shoulder down, back elbow tucked to there side and the bat at a 90 degree angle to the ground as they start the swing.