Do you know for certain that the mother thought everything was fine? Did she comment aloud about the incident? Or are you interpreting her silence as agreement with the screener's actions?

I can easily see a scenario where the mother disagreed with the actions, but decided that the best thing to do in that situation was to minimize any interactions with the TSO by remaining silent and proceeding through the checkpoint as quickly as possible. Not everyone has the option of staging a civil rights protest at a given moment. And given that she had her two minor children with her, she may have had more reason not to protest.

Just because someone is silent before an authority, or offers a smiling face, doesn't mean they agree with that authority.

As someone once said: never try to teach a pig to dance, for it frustrates you and annoys the pig.