As I understand it, only her Bishop has the right to excommunicate her. When she is receiving Communion in other dioceses, those priests are on their own. Having been an Eucharistic minister, I can tell you that it would be very awkward. How would the Eucharistic minister (who is not always the priest) know whether she'd repented and received absolution from her priest and the EM hadn't been told? And there is a long line beind her. It would be a logistical nightmare from a practical standpoint. This is just a personal observation -- not an official Catholic teaching.
Of course when the line is stopped and Nancy is abruptly escorted from the church by the ushers, the dancing and cheering of the other parishioners would be hard to control. That might cause "scandal" in the press. Catholics don't approve of scandal and try to avoid it at all costs.
