Whoa. It seems like we have a few problems here.
At that point during the Mass, nobody should be around the altar except for the celebrant(s), deacon(s), and altar ministers. A female Episcopalian minister, while perhaps considered a minister by those of her own persuasion, would certainly not be considered a duly instituted “altar minister” in the eyes of the Church. And obviously, she would neither be a celebrant nor deacon, either. That means that her role during that point is akin to that of the congregation which at least means that she would have to be kneeling somewhere removed from the sanctuary.
As for her holding out her hands “as if to con-celebrate,” this is a very grave liturgical abuse and the priest who permitted this (if he did permit it) would be liable to canonical penalty.
According to the Code of Canon Law:Can. 907 In the eucharistic celebration deacons and lay persons are not permitted to offer prayers, especially the eucharistic prayer, or to perform actions which are proper to the celebrating priest.
Can. 908 Catholic priests are forbidden to concelebrate the Eucharist with priests or ministers of Churches or ecclesial communities which do not have full communion with the Catholic Church.
Furthermore, his communicating her was a grave risk of scandal and not to mention, a violation of the Church’s not-unclear guidelines for reception of Holy Communion–most disingenuous on her part and sacrilegious on the part of the priest.