Marital sex just needs to be varied. If the couple won't do it together, then clearly they will still do it secretly each separately! I think this home variation is acceptable, in any case it is not as extraordinary as entertaining a large group of swingers. My wife and I once invited me to one of these, against her this clip is just sex puritanical family!
That's how the mother took advantage of the situation. She put her ass on the line for her daughter. Now they'll mistakenly think her daughter's a whore. And even her classmates in the bathroom will pull it on her.