Very good. I can't help but thinking at 15 her world is turned upside down because of a head injury. Why wouldn't she be depressed?

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.

PCS is a frequent cause of depression, regardless of the happiness or sadness in one's life. My psychiatrist explained depression as when the brain gets polluted with the toxic waste from stress. That stress can be from positive life experiences or negative life experiences. We all know how PCS can be an overwhelmingly negative life experience. Add in the lack of social support, physical activity and for a teen, hormones trying to find a balance, and depression should be considered a given.

One of the struggles the PCS brain has is in maintaining the blood brain barrier. Those struggles are why many PCS symptoms show up a few days to weeks after the impact. Immediately after the trauma, the brain tries to strengthen the blood brain barrier. That extra strength does not last long, eventually allowing the toxins to effect the brain. This is when symptoms can start to roar. This same weakening can lead to depression.

This depression-concussion link is well reported even though some neuro psychs try to dismiss it. As discussed in the links posted by Lara, attorney Gordon Johnson warns about this bias held by many neuro-psychs.

But, depression is still not a valid excuse for all of her struggles.