In the post Vatican II era, introduction of Extraordinary Eucharistic ministers was permitted, which would include sisters and theoretically nuns.
Since nuns are cloistered (sisters are not) they would be less likely to be seen engaging in this practice because generally they are traditional and rely on the ordained priest to serve them at Mass.
This practice of lay Eucharistic ministers is arguably an ill conceived novelty, as before Vatican II, only priests could touch the Eucharist — because only they had hands consecrated for this purpose, which is actually still the case. In Baptism, however, all Catholics have their tongue consecrated to receive the Eucharist, the hands are not included in this Sacrament.
Part of the argument against this novel practice is that the role of the priest is diminished by allowing anyone to distribute Holy Communion. Since we have seen a decline in faith in the Real Presence over the last several decades, I think the Church should examine some of Her practices to see which ones help reinforce belief and which don't. This may be one of those . . . we'll just have to see how it plays out.