Well, the wearing black, calling herself Martyr, and kidnapping Attilan royalty at swordpoint didn't start until after the run-in with Oblivion. Hard to fault anyone a little insanity when they've got the near-omnipotent embodiment of nonexistence chomping on their brain. Honestly, the only thing about her behavior here that seems weird is that she bothers to apologize.
(I do kind of wonder why the Guardians just sort of ignored the six million neon warning signs that led up to this, but I suppose they *have* been extremely busy.)