Should i be concerned about my daughter, who had her wisdom teeth removed on december 9 and has been complaining of jaw stiffness and difficulty opening her mouth?

If she can't open her mouth due to pain and stiffness and she can do it after taking a pain pill, you should not concern much. If she does not have any pain but not able to open her mouth due to stiffness, she should try her best to open her mouth against the stiffness with massaging the TMJs at the same time. As long as she is able to eat and drink she will be fine sooner or later.

Only your practitioner knows the extent of your procedure and thus the anticipated post-surgical course of recovery. How long post surgery? Is she on antibiotics? Are stitches still present? Your Dentist or Oral Surgeon, whoever did the procedure, is responsible for your post-surgical care. Call him/her.