Well, I'll share my own F!Cousland's perspective, as she doesn't always see eye to eye with Alistair, as I headcannon a lot of this:
1) Alistair blames death of Cailan, Duncan, GW's and army at Ostagar on Loghain. Cousland disagrees on some of the details, giving a more nuanced analysis of the situation. Alistair may or may not agree, but it's largely a moot point, for reasons below.
2) Alistair doesn't trust Anora. Cousland is very, very angry with her for various reasons. Then again, Cousland is also angry with a great deal of the Ferelden elite, who seem not to care a whit that the Teyrn of Highever and his family were betrayed and murdered in cold blood. So much for oaths and fealty.
3) Alistair does not wish to be king, initially. Cousland, however, absolutely wants to be Queen, and talks him into it. None among the eligible elite are worthy in her eyes to marry. Alistair is a bastard, but has Maric's blood, which says nothing of his amiable personality. I doubt in a more realistic setting that he would actually be King: it's much more likely that Cousland would become Queen Regnant with Alistair as Prince Consort, since she's full blooded Cousland, and of higher birth than any other noble in the Landsmeet other than her brother.
4) Holds Grey Wardens with high standards. Cousland has a more realistic perspective on the order.
These last two points are all Cousland, and they settle the matter in her mind:
5) Howe. Loghain and Howe. Need I say more? Hell, Loghain, Howe, Cauthrien and Anora.
Loghain, by the time of the Landsmeet, has made things very, very personal for Cousland. Anora, Loghain and Howe have, at one point or another, all conspired against Cousland to either kill, frame, or imprison/torture in Fort Drakon (where she would likely be raped) for their own ends. Cousland, who has been running around the country for a year, trying to save it from the Darkspawn, is incredibly incensed at Loghain for all of this, and has had enough. She's tired of being called a traitor or churl, tired of being chased by assassins, and dealing with people who simply won't get out of her way. The final straw is when Loghain accuses her of killing Howe, calling it "no justice to butcher a man in his home", which is exactly the sentiment she holds for her father, her mother, her sister in law and nephew, not to mention all of her friends and their families back in the North, who are probably piled up in a mound, unburned, unsung and unavenged, since Loghain couldn't be bothered to do his job. It's the most hypocritical, infuriating, and completely ridiculous garbage she's ever heard, and she's not about to hear any more.
By the end of the Landsmeet, Alistair doesn't kill Loghain. She does.