Myself totally opposed to young girls or boys for that matter using weights, even light ones. My preference is body weight exercises, push-ups, pull-ups, one legged squats, swimmers, side lunges, back lunges, and many more and all sorts of devious variations thereof.
But then again I come from a military, i.e., Infantry 15 years, back ground and have seen guys who can bench 250 but can't do 5 pull ups. Is it that they are not strong enough, no, it is a mental thing. Body weight exercise teaches the ability to move your body using your strength and building toughness of the mind.
And I am yet to see anyone tear out a rotator cuff doing push-ups.
Java's Red Cord workout is the hardest core workout my 15 year old has ever had. In fact, my 17 year old basketball player (son) refuses to do it because it's too hard -- even knowing it would increase his vertical. It's because only one of my three kids is in what Java calls his 10%.
It's worth the investment!