Andresm. wrote: ... why did the girl die? Was it for the medicine? Or why was not it a nightblood? Was Luna's daughter? or sister?
The girl, Adria, didn't die "for the medicine". She died of acute radiation syndrome (ARS), just like the rest of Luna's clan. Adria was the only one given the medicine, but it was given too late to save her life. (Chances are, it was already too late by the time they reached Arkadia.) Though it's possible that she was related to Luna, it's more likely she was an orphan. (It's mentioned in "Red Sky at Morning" that Luna's clan takes in orphans.) If the girl was a Nightblood, chances are she would've gotten better (with or without the medicine), but she wasn't a Nightblood.