I wouldn't really say that she drove Rowan and Maric apart. Rowan was clearly feeling something for Loghain long before Katriel turned up, and it was only her betrothal to Maric that held her back. The night when she's wearing her dress and hears Katriel and Maric, then finds Loghain, we can see clearly just how torn she is. When she pushes Loghain away and says "I cannot... I will not be that woman." She wouldn't break her promise to Maric, however much she wanted Loghain. There was no happily ever after for any of those four (I'm including Katriel in this).
As for Katriel, that's a little more complicated. She infiltrated the rebel army, fell for Maric, turned on Severan, refused to murder Maric, and then his life. She then lead Maric, Loghain, and Rowan back to the Rebel army, completely turned on Severan (even leaving instructions on how to kill him), and returned to Maric, knowing she'd been found out. But ultimately she was doing a job, and unlike many who stood against Maric, like those who killed his mother, she owed no loyalty to him when she arrived. I can't really hate her for that, not when she went back to Gwaren to face Maric.
Personally, I consider Loghain more of a traitor than Katriel, at least as far as Maric goes. Loghain betrayed him more than once, keeping back information about Katriel which might have stopped Maric simply running her through, then forcing Rowan to go to Maric afterwards, after he'd slept with her. I respect that he forced them together for Fereldan, obeying the promise he gave to put Fereldan before Maric, but still, it was a seriously cold move. And, I'll grant you, a huge sacrifice on his part. Loghain gave up or lost everything he had in The Stolen Throne, and knowing that makes me hate him a lot less for what he did in Origins.