TOTP can be used today to authenticate a couple to each other over an untrusted medium.

It’s rather high friction; you have to set it up in advance, and then read a six digit number over the phone. And I am not sure that it mitigates the threats… in this situation, I suspect it wouldn’t. It could even make the situation worse if the daughter is genuinely in trouble but can’t access the authenticator.

But I can’t think of a better solution. Any other ideas?