I'm currently reading the book "World without end" by Ken Follet and he mentions that the local bishop gave the nuns authority to perform the sacrament of confession and last rights do to the massive number of priests who died do to the plague. Is there any truth to this or was it all made up?
I have never seen an example of it.
This would be tantamount to promoting those nuns to priests. In the 12th century, abbesses were actually prohibited from hearing the confessions of their own nuns by explicit papal injunction.
It is true that, in theory, at moments of utmost need a layperson can perform the necessary final sacraments, but usually this was confined to extreme unction, and even then there was still a lot of theological dispute as to if it was actually effective.
I'm not going to say this never happened, because who knows for sure, but it seems very unlikely.
According to Catholic sacramental theology, only a priest is ontologically capable of performing these sacraments, and women are not ontologically capable of being made priests (argue what you will, but I'm towing the party line here)... Lowing the standards for ordination is one thing; ordaining women (or treating laypeople of either gender as ordained) is qualitatively different.
So while it could have been officially sanctioned by a rogue bishop, it would have nonetheless been what we call "simulating a sacrament," rather than an actual sacrament. The only sacrament a nun is ontologically capable of performing is be baptism (like all the rest of us laypersons).
FWIW, I have an M.A. in Catholic liturgical studies, have been attending conferences for a few years (on all sides of the ideological spectrum), and copyedit a major Catholic liturgical journal. I've never even heard this particular theory before, which only adds to my extreme skepticism of its plausibility.
From The register of Ralph of Shrewsbury, Bishop of Bath and Wells, 1329-1363:
2130. The mandate is addressed to all rectors, vicars, and priests that they should make known to the laity that on account of the spread of the plague — con- tagium pestilentiae modemi temporis undique se dilatans — they need not hesitate if they are overtaken with the sickness and cannot make confession to a priest, to confess to one another, and even to a woman — quod predicta confessio facta laico in casu praemisso juxta doctrinam ecclesiae et canonica instituta ad remissionem peccatorum eis multum salubris esse potent et
So, at least in that diocese, under that bishop, it was permissible for people to confess to laypeople, including women.