The Magic does tender occasionally at St. Thomas on the Eastern. It is based on how many ships are in port (they roatate tendering duties at this point). More often than not they do dock, but there is always a chance. The Magic (as do all the other ships visiting) always tenders at Grand Cayman.
Your mom should be fine - they are used to dealing with just about anything and some of the tenders are very large multi-deck ones. You may have to wait a little while for the right one, but I'm sure they'll take care of you.