Question

An acquaintance of mine, a Torah scholar, married the daughter of an ignoramus.
At his father-in-law’s home, “Judaism” means that the women keep their heads permanently shaved before immersion, don’t eat machine-made matzah, and a few other “essentials” of the religion like that.
That’s basically it.
After they had several children, the kollel fellow studied the topic,
and they reached the conclusion that there is no need to shave one’s head before immersion, and his wife was happy to be rid of something that, in her view, was very burdensome and humiliating.
But she can’t come to her father’s house for fear that some hair might peek out, so she only comes wearing a wig, which is cumbersome and uncomfortable.
Lately the father has started coming to their home without prior notice.
He just knocks on the door,
comes in, takes a drink out of the fridge, stands there and shouts: how can you drink something with such a lousy certification? (It’s mehadrin, but not from his circle.)
And she runs to the room to switch to a wig so that, God forbid, he shouldn’t see that she isn’t shaved according to his religion.
 
What can be done about such conduct?