I don't think so, this time. Finn had changed or MC had managed to change the opinion of Medb and Finn about peace being possible (and desirable) it would be odd if Finn then went and attacked without cause. My theory, admittedly based on not much, is that she went as a peace envoy to the Templars and someone - or some group - that didn't want peace killed her.
But, in a way, it's the things you dislike about Finn that made her my favorite. In a world where everyone around MC was harboring secrets, and politicking, and plotting - Finn (for good or ill) wore her heart on her sleeve. There was no need to wonder what she wast thinking because she'd tell you. If she was plotting against you, you'd know because she'd be standing in front of you with a sword telling you to prepare to meet your maker. If she suddenly decided she was attracted to you, you'd know because she'd invite you to her favorite, secret spot to go skinny dipping. If you wanted her opinion, she'd tell you and it would never occur to her to soften the blow. She was a direct contrast to everyone else around MC except for Kate, Elia, and Jessica - who might be honest but who know even less about that world than MC does.