Watching The Sound of Music for the umpteenth time triggered this questions (which is not about the movie, per se: )
Maria walks to the cathedral with all her nun friends, into an alcove behind a fence She then goes through the fence and walks down the aisle; the nuns stay behind and literally watch through a locked fence. It very much looks like there’s a line that they can’t cross.
I spent 8 years in parochial school so I’m nun-adjacent, and I don’t recall any church prohibitions on nuns attending a wedding (and obviously there’s no rules against them entering a church).
And such religious rules often have “Except when necessary” exclusions. During the pandemic, in Canada, we had a pair of Sikh brothers, who were doctors. They were faced with the problem of a religion that requires them to not shave their beards, and the medical requirement to be clean shaven so that their masks would work properly. Faced with the unavoidable choice between observance and practicality, they shaved their beards.
I suspect that sabotaging a Nazi is a bit more important than attending a wedding, so they accepted this minor violation of their rules.
All we see is the Nazis unable to start their cars, followed by a scene of the nuns saying “Reverend Mother, I have sinned” and displaying two distributor caps. So they knew & confessed that they had sinned.
And we’re all hoping that little jerk Rolfe got killed at Stalingrad, right?