Kotor Campaign guide.
She wouldn't need to reveal herself.
And perhaps not beheading, but she's healed grevious death wounds before.
Ok I assume you are talking about, Revitalize right? Because looking at the guide, her power list doesn't show her to have that ability. (Unless it's in another guide.)
Even then the ability only lists to dealing with wounds, exhaustion or unconsciousness.
It's not listed she has that ability and even if she does, that isn't gonna help when a death blow comes upon Malgus and yeah she may bring him back but why? More to that, why would she even help him anyway? This is a 4 way fight and I don't think Malgus would take her help anyhow, they are all fighting against eachother. Plus she is really gonna waste time with helping Malgus out during all this? I don't think so.