The fact that she is a Medical Assistant has nothing to do with why she can not bill for what she is doing. Medical Assistants can remove sutures, however, the fact that suture removals are included in the "global surgical package" makes it noncompliant with coding and billing guidelines to bill for the suture removal.
However, if you were removing sutures placed by another provider, (not of the same practice), then you could definitely bill a 99211.
Some helpful documentation:
http://www.aafp.org/fpm/2000/0300/p21.html#fpm20000300p21-sa3
Hope this helps.