First off, have your mom get a second opinion. Always.
I cringe because my shoulder used to look like that for a while. I fell the wrong - very wrong - way during a karate match in my late teens.
From what I can gather, it looks like it MAY be a AC (acromioclavicular) joint separation.
If you fall on your shoulder, the force pushes hard on the scapula. The collarbone is attached to your ribcage and can't shift with the scapula and the ligaments in the joint get ruptured, or torn.
The treatment depends on the degree of the separation. Usually, from what I remember reading, no matter what degree, that bump is very common. I had it, sat in a sling for a while, and it got better. I knew a guy who tore up his AC joint, had surgery, and he still had the bump - though not as bad.
Of course, I am not a Dr., and am doing my best with your photo.
Best of luck.