'Sound of Music' rip-off
I can only imagine that this movie must have seemed like sure-fire gold in the years immediately following Julie Andrews' portrayal of a nun-gone-astray in "The Sound of Music" - particularly since the Broadway musical was also based on a true story.
In "Nun" there are even characters that mirror "Music" as far as nuns go: Agnes Moorehead and Greer Garson function in the same roles as Portia Nelson and Peggy White in "Music": one nun is totally disapproving, while the Mother Superior is all-knowing and tolerant.
And of course - Julie and Debbie both play guitars as part of their roles.
"Don't call me 'honey', mac."
"Don't call me 'mac'... HONEY!"