Last issue she went into that body, was possesed by malice, then she left/was expelled once more by malice wich caused her to jump around the multiverse confused, her body was still possesed when the captain corps removed her soul.
All of this caused her to be in the state we saw her in, when she had the oportunity she ran away from the body possesed by malice and became some sort of psychic/magical specter burning away her surroundings, creating ilusions to put people away
She praticaly was haunting that well, changing her form like an incoporal presence would, at the whim of her twisted emotions
like many ghosts in fantasy (wich the white dress helps convey is what tini is trying to invoke) their moment of death can shatter their memories/perceptions of their lives, leaving them incomplete and agressive just how betsy was, until they regain a missing piece, regaining clarity and stoping their agressive lashing out.
srs she was turning into a monster of purple fire, she clearly wasn't in her proper state of mind, this was a poltergeist betsy moment