Hello, The lump which you have mentioned is likely a bone cyst or a ganglion. Its a benign condition and at her age, its quite unlikely to be a cancer. Please do not get worried. You must get an X ray of her wrist to know where it is arising from. Some times, a close examination can be helpful in identifying the cause and course of the swelling. If the lump is not increasing in size nor giving rise to pain then I shall suggest that you wait and watch. If either of the two things are occurring then it shall be advisable to seek the opinion of either an orthopedician or Surgeon. Hope this helps. Please write back for further queries. Wishing you good health.