Don't know if you have to play the doctor card just yet, as it sounds like you've only tried one or two exercises out of many. The best advice I can give you is to start her on a regular flexibility program that places priority on the muscles that restrict mobility rather that repeating the desired motion hoping for results.
Here's a brief decription of muscles and exercises for them, all of which should be done pain free with low resistance and high repitition........
Chest muscles and bicepts......Using a 4 to 5 foot length of broom stick, place both hands near opposite ends of the stick with the fingers in an "over grip". Starting with the stick in front and at the hips, slowly raise the stick with extended arms and shoulders (shrugged in the direction of the stick) up in a cicular motion that takes the stick over head and behind her until the stick is down at hip height.....reverse the motion using the same extended arm and shoulder positioning until the stick comes to rest in front at the hips. This should be done with a fluid motion absent any sudden hitches or jerks, and both sides need to rotate at the same pace.
Do this front-to-back-to-front cycle 20 to 30 times starting with the hands placed very far apart, and moving slightly closer together until it feels like she's getting a stretch. Continue with at least ten more cycles with the hands in this position, moving hands closer only when the stretch feeling subsides. Stop the exercise immediately if there is any pain, and try again the next session.
Triceps........Standing french curls with a single dumbell. Look for a reference exercise on you tube, and modify it to place the elbows as far back alongside/behind her ears as possible. Maintain the elbow position through-out the exercise. Use a weight light enough to allow at least ten pain free repetitions that tire, but don't exhaust her tricepts.
Tricepts.......Same exercise as above but with one hand and less weight. Change the direction of the arm swing from the front to back used in the first exercise, to an overhead to a crossing behind the head motion that places the weight just behind the opposite shoulder before returning to the stretched overhead position. Same numbers and attitude as tha above exercise.
Lattimus......Modify tricept #2 execise......laying on side with arm extended and weight positioned straight above her shoulder. Slowly lower the weight with a straight arm that reaches behind her head as far beyong thew opposite shoulder as possible. In that position perform a "french curl" motion, and when the arm returns to the extended position move the arm up through the same arc to end with the weight at the original start position.
Intercoastal muscles.....Feet elevated bridges with a slow rocking motion that moves her shoulders from forward of her hands to behind her hands. This should concentrate most of the stretching sensation into her rib cage. Use 20 to 30 cycles over the span of 60 to 90 seconds.
This series of exercises should do alot for her shoulder flexibilty and strength. The series should be done no less than two times every other day.
But the more the better, it keeps her from getting bored, so I like a lot of these! We have been doing to overhead stretch with broomstick, the french curls look interesting as do the crossing over ones. We do similar but this would be good to get into rotation. We have a similar one to the lattimus except she lays on a pool noodle running down the length of her spine (it's a good thoracic spine stretch) and does the lifts overhead to the floor with straight arms. But I think the crossing over will be a big help. 
and she loves gymnastics so very much.
