1. More rest won't really help. If she took 4 weeks off (or mostly) off, then more rest won't fix any problems, just lesson the pain, which will return when she starts swinging again. It is hard to know exactly, because I don't know the amount of swings she took so far in the early practice/matches.
2. Periodic rest would help, and beyond that, hitting at 75% in practice is key; just enough force to work on technique, but not strain the shoulder.
3. A orthopedic sports doctor will do an evaluation and if concerned will schedule an MRI - A MRI is the only way to know if something is torn inside the shoulder. If your insurance will cover, getting a MRI at least will give you a yes/no on any damage to the shoulder.
4. Shoulder issues can make a college coach hesitate - Just the nature of her position and the pressure of recruiting. DI's are not keen on scholarshipping an athlete with injury history, and if they do, they are not hesitant to cut them after their freshman year if they still have issues.
5. Ice is good and ice will be her best friend in staying healthy when she gets to college! I strongly suggest she get into a daily routine with the shoulder bands (thera-bands) because it is a huge help in building up shoulder stability/strength through the smaller muscles. The routine only takes about 10 minutes max and almost every college team has their hitters on a routine as preventative.
My instinct is that with being smart in practices, letting the shoulder rest a day or two week, icing always and then doing a daily shoulder band routine, she will start to see the soreness dissipate! If it does not, then you have to go see an orthopedic surgeon to get an MRI to get clarity!