Exactly, this isn't a chemical imbalance depression it's just being sad about what's going on around her. It's a completely normal reaction. I am going through the same process at age 26. It is very difficult to deal with PCS during youth because we are normally so active and then our world just stops.

Best advice is to exercise if she can, eat healthy, and stay positive! It seems she has a supportive mother at least and that is another important thing.

Hang in there! Supposedly, it gets better over time if you take the right precautions.