So a 44cm is too tall for someone 5'2" but your daughter rides a 49cm road bike... How is converting a 44cm mountain bike going to make it bigger than a 49cm road bike?

Again; I'm very sorry you only found frames with 5+ inches longer on the top tube than the seat tube. Not all vintage mountain bikes frames are like that. Most of the time frames with no more than 3" of top tube difference can be brought to heel by just swapping the stem.

Crank length can be challenging and is in a different category. My daughter seems to do OK on 170mm cranks (we have done some long touring with her using those) but it seems to biomechanically work better on 165mm. Every person is different and even at 5'2" some don't have issues with longer cranks while others get hurt with them.