I’m a guy (as the name says) and would not have dared to ask R’ Shach a question on a Ramban (or Tosfos) if I would of had a chance to meet him! How about a Bracha that you should have children who are Yarai Shmayim (let alone get married)! Asking a question of that nature is for a personal Rebbe, and R’Shach was the GADOL HADOR.
It is a general problem (as JO JO pointed out in the post on kiddashim) of Penay Hador K’Penay HaKelev. The Gedolim are people who we stand in AWE from, not talk to them ask equals or even only one step above us.
(I would not blame the girls in this case as their “teacher” (probably the sort who says that you are eating Traife if you don’t have two sinks) told them this was the right thing to do, instead of the teacher asking her Rebbe or husband.)