I can tell you from personal experience with my DD that you should go back and re-read Austin's post and the articles he linked to. Also read the Throwing thread referenced above. Re-read the throwing thread again until you understand the proper sequence of the throwing motion or you will most likely only be hurting your DD more. Here is another article with a similar take on throwing.
How do I know this works? My DD (10 years old) has always had a strong arm, but I taught her the dreaded L and face the ball away crap that is commonly taught. She had frequent shoulder and elbow pain, and slipped into side arm because it didn't hurt as much. After about a year of working on her sequence, ala Austin/Tewks' direction, she now throws bullets from home to 2nd. No side arm, keeping the hand back prior to front leg ER with great arm whip and no pushing. Her mantra is now 'Thou shalt not steal', and you'd better be fast if you try. Although not many do after the 1st inning. Oh, did I mention that she has absolutely 0 pain and can throw all day long.
I have recently introduced thoracic extension (TE) and we do long throws 4-5 times a week out to 80+ feet (hey, she's only 10). No rainbows, pretty accurate and no pain.
Understand the sequence and lose the L.
Yes, Yes, Yes. A moderator really should make the Throwing thread a Sticky.