I am Anglican and not Catholic. But I think the answer from a RC p.o.v. would be:
- The Anglican priest’s orders are probably not valid, and even if valid are not licit. (Anglican orders were declared invalid some centuries ago, by one of the Popes Leo I believe. Due to some change in Anglican rubrics in the way Holy Order were conferred. (The rubrics were eventually changed back, but by that time it is said that there was no living person in Anglicanism who still had valid orders or the capacity to pass them on to other Anglican priests). However, many Anglican priests and bishops have in the past many decades been co-ordained by Old Catholics, former Catholic priests who became Anglicans, or vagante Orthodox, whose orders would be ‘valid but illicit’). One cannot receive communion from a priest with valid orders who is acting as a priest ‘illicitly’.
- The Anglican Church does not officially teach the Real Presence in the Eucharist. (Nor do they deny it explicitly: about half of all Anglicans accept it, and about half probably don’t). The RCC would not be comfortable with this ambiguity of doctrine.
- To receive Eucharist in a non-Catholic church would be tantamont to acknowledging that one is in full communion with a Christian body which is in fact NOT in communion with the Roman Catholic Church.
All of which, being said, does not mean that your wife incurred any penalty of excommunication: assuming she was in sincere doubt as to what to do and acted with the intent to avoid causing needless offense. (In some cases, of course, one must act according the principles of faith and a properly-formed conscience, even if offense occurs: I am simply suggesting that your wife was caught off-guard and unprepared and acted as she saw best at the moment, for which there MAY HAVE BEEN no sin involved. Depends on other factors of course). She DOES have a responsibility to inform herself and properly form her conscience against a future recurrence of the situation, but assuming good faith on her part, no mortal sin occurred IN THIS INSTANCE. I think I am speaking accurately. Let’s see if someone blasts my comments out of the water.
This said: what did your wife think of the Anglican service?