What is the the procedure for such an situation? I feel it should not have been dealt with at the moment to spare an interested person the akwardness. At a later date and more private setting, her study conducted should address the issue.There is no real procedure to handle this and the plate and cup passers should not question whom should or should not partake.
Most people "invited" know the procedure and those that don't should have been carefully briefed before the occasion to NOT PARTAKE.
A most embarrasing moment for me was a few years ago.My MIL was sitting next to us with her "study" When the bread was passed the study started to partake as she was used to.My MIL said(quite loudly) NO...NO don't do that. The study dropped the wafer back and didn't even think of touching the wine. Never did see the study after that