The fiberglass of my mom on her fractured ankle is no longer tight as before. what it indicates?

Decreased edema: She has decreased swelling and the cast is now loose. If she can move her ankle around or is having discomfort the cast will need to be replaced.

Swelling has gone: Likely there was still a significant amount of swelling when the cast was put on. The swelling has healed, so the cast is loose. Or... If the cast has been in place for a long time, atrophy (shrinking of the muscle) can occur. Best thing is to return to the doctor to evaluate and replace the cast if necessary.

Swelling reduced: So now the cast is not as tight. She should let her doctor know as movement within the cast can possibly cause rubbing and irritation and create a skin abrasion.

Swelling: Is going down. May need a new cast. Check with your dr.