What do the nuns do all day? Why do they seem to thrive on "picking on" Maria? How come they're so obsessed with Maria? So obsessed, that they make up a song about it ("Maria"), which they sing at her wedding.

When Maria goes back to the abbey in her confused state, the Reverend Mother tries to learn the reason for her unhappiness and confusion. The Reverend Mother asks Sister Margareta to bring Maria to her office. She proceeds to ask Maria the cause of her leaving the Von Trapp home. Maria, after several replies, finally says "I can't face him again." The Reverend Mother, shocked, almost shouts, "Him?" She then asks Sister Margareta who has been standing by the door to leave. We ask, why did the Reverend Mother bother asking Sister Margareta to leave? It's not as if Sister Margareta does not already know where the conversation is going to go. She will be able to piece Maria's statements together and figure out that the "him" is none other than the dashing Captain himself. The Reverend Mother should have had more tact and asked Sister Margareta to leave earlier.

During the wedding, why are the nuns kept out of the wedding ceremony? We see them standing behind a gate, smiling and happy. (Sister Margareta must have been extra-happy because she is right in her guess.)
NOTE 1

The Von Trapps, after leaving the folk festival, hide in the abbey. The Nazis follow them there but they are unable to pursue them further because their cars wouldn't start. We learn that the nuns have tampered with the cars. How did the nuns learn so much about automotive mechanics that they are able to pick out the right part to remove?
NOTE 2