The "terrible triad" is a term that can be applied to many joints including the shoulder, knee, or elbow. It always refers to three areas of damage or injury in the same joint.

For example the terrible triad for the shoulder includes shoulder dislocation, nerve injury, and tendon tear. In the knee, it's ligament and cartilage damage. In all cases, the joint is unstable and needs surgical intervention.

In the elbow the terrible triad refers to ligament tears, bone fractures, and dislocation. More specifically, there's a posterior dislocation of the elbow joint with fracture of both the radial head and the coronoid process.

The radial head is the top of the radius (one of two forearm bones). The coronoid process is a lip of bone at the top of the ulna (the other forearm bone) that is part of the elbow joint.

Treatment of the terrible triad for any joint is complex and lengthy. In a young person of your daughter's age the chances of recovery are much better than in an older adult.