I apologize for bringing this up again, considering my previous thread was locked. But I found out more about my wife’s experience while she was out-of-town.
It turns out that the congregants of the church she attended actually did get up and move to a new pew when she, my daughter, and mother-in-law sat down. They were isolated by a buffer zone around them. :shrug:
I looked it up on the 'net and the parish is part of the Priestly Fraternity of St. Peter.
I don’t know if the FSSP Mass is like other Tridentine Masses, or if it is somewhat different yet again.