It would be highly unlikely that bruising alone would be a sign of leukemia. Active young people can bruise without knowing the trauma that caused it. Should this problem continue I would take her to her physician for an evaluation.

There are many possible causes of easy bruising, most of which are benign. Leukemia would be a rare cause, but more common causes include use of aspirin, fish oil supplements, or benign disorders that increase bleeding propensity. A thorough hematology evaluation would help determine the cause of bruising and whether any treatment is needed.

She needs a blood test and coagulation test to find the cause to be treated. Continue follow up with her doctor.