Weird Harold wrote: More likely is C) An entire Admiral's Staff realized that she was irrational and her refusal to surrender was going to get them killed for no gain. Manticore didn't press the issue of who pulled the trigger because it was a joint decision to dispose of a threat to their survival.
It wouldn't have taken any sort of MAlign influence to get Adm Crandall a bullet to the head; Adm Crandall was more than capable of earning that end all by herself. There are several POVs from a staff member highlighting Adm Crandall's disconnect with reality.
Adm. Crandall gets a lot of stick for her idiocy, but in my opinion it's unjustified. From the text, she's arrogant, ignorant of Manty capabilities, and the arrogance leads her to underestimate the depth of her ignorance. And she has "the disposition of a grizzly bear with hemorrhoids trying to pass pinecones."

Nevertheless, when members of her staff warn her of possible threats, she takes their counsel under consideration. When presented with evidence for the Manties' FTLcom, ultra-long-range missiles, etc. she accepts them as real.
Crandall's ill-served by her chief of staff, who's the real idiot. At one point, he himself suggests, "Maybe they think they can pull off some sort of 'ambush!'" Then -- moments later -- he ridicules the idea that what the Manties are "really trying to do is to convince us they're even weaker than they actually are". In other words, to lure the Sollies into some sort of ambush!
When last seen, Crandall is fully aware of her fleet's dire situation:
"I doubt even Manties would have fired missiles they can't control." Despite her own shock, despite her truculence and undeniable arrogance, Sandra Crandall's eyes were dark with a refusal to hide behind simple denial. "You may be right about the accuracy penalty, but if they can throw enough salvos this size, even crappy accuracy's going to rip our ass off."
Bautista's eyes went even wider at her harsh-voiced admission. He opened his mouth once more, as if to say something, but no words came, and he closed it again.
Crandall never even noticed.
So I don't see the "refusal to surrender was going to get them killed for no gain." I also don't see the point of fragging her on a broken ship which was unable to communicate anyway. O'Cleary took over, and surrendered less than two minutes after the first salvo struck, because neither Crandall's nor her 2nd in command's ships were operational.