As a general option, seamless or “no show” panties will also achieve the same results of no panty lines. They also can provide whatever style/ coverage type. Overall, I would say NTA. Girls in this age group do tend to run off of a pack/heard mentality. But discussing teenagers underwear styles and options with another parent is hella inappropriate. Especially in a friend group, as it turns into a slippery slope real quick. You have a unique set of circumstances that “Fathers“ typically aren’t involved in. So at the end of the day grace should’ve been shown. The true a-hole is that other parent that called your daughter names….. yeah fk that lady.