I have no trouble believing that Zina burned the clothes accidentally-on-purpose. Doroshenko's presence was clearly very difficult for her. I don't understand why they didn't tell her he was coming until the last minute, that's just mean.
I don't think it does any good to pretend that there weren't frictions and interpersonal difficulties between the hikers, whether that's the Zina-Doroshenko issue, Lyuda's moodiness, Kolevatov's argumentativeness, or Dyatlov's bossiness. Things like that matter less when everything's going well, but can matter a lot when people are tired and uncomfortable. It doesn't mean it had anything to do with their deaths.
Reading Zina's letters is very moving. The extra insight into the hikers' lives and characters these documents give us is really special.