First of all it is actually way harder to get hormonal treatment than you'd think (as it should be). Especially if you're underage. I think most parents wouldn't consent to medicating their children in that manner anyways.

But more importantly - you don't need to be diagnosed with anything to have people around you show support. Dad could sit down and try to emphasize and understand where the daughter is coming from instead of putting loads of effort into humiliating her which only served to invalidate her feelings, trans or not. Even if she was just confused and not trans, all she learnt from dad is that her feelings are not important or worth sharing.

If your kid comes up to you and says they're depressed, is your first response to start making fun of them until they are officially diagnosed? What the fuck kind of parenting is that? That's how you create emotionally stunted adults. Meet your kid where they're at, level with them, take their feelings seriously, but set healthy and reasonable boundaries. It really doesn't need to be more complicated than that.