This may or may not be true. Very little instruction on the view path and action of training the body has currently come down to us through any of the Christian traditions. It might be there, but it is generally aphoristic, a series of maxims which are removed from direct practical instruction.
As to the nun being out of line, I have to agree with you as far as the church is concerned. As to whether individuals need to make such choices , and live with them, I think they should have the right to do so. Her choice may not have necessarily been a mistake. Celtic feminine wisdom is very much alive and well in the Scottish church, as is the wisdom of Roman women, especially in the Italian version. The church has to say it is wrong, but compassion is a tricky subject, best left to the decision of those actually on its battlefield of suffering.
The way Christ related to Mary Magdalene is a good example of this dynamic.Several of the disciples disagreed with him.
That is all I will have to say on this touchy subject.
I see your point. I hope someone will correct me if I am wrong (HILDY? ;-), but I think Christ said feed the spirit and starve the flesh. Like I said, I may be wrong on who said it.