Jaina's in an odd place because she's still working her way through her emotional and mental breakdown from the climax of Tides of War. She's willing to give peace a chance, but tends toward hardline responses when the Horde tries to abuse that, as seen when she expels the Sunreavers from Dalaran and arrests many of them, and her stance toward the Horde (that it should no longer be allowed to self-govern) is largely justifiable insofar as the orcs have a proven track record of warmongering and refusing peaceful solutions--here, Thrall, Eitrigg, and Saurfang are the exception rather than the rule. Seems she doesn't trust Vol'jin much, either, and again for fairly good reason (every time she starts trusting the Horde, lately, someone goes out of their way to screw her over).
By the same token, though, when someone from the Horde goes out of their way to try making peace work, she's generally receptive. At the Isle of Thunder, when Taran Zhu finally gets Jaina and Lor'themar talking for five seconds instead of preparing to beat the shit out of each other, she realizes that he's out to take Garrosh down same as her (to whit, when she claims peace won't happen while Garrosh runs the show, Lor'themar responds by noting that's exactly why he doesn't want to waste troops on the Isle, showing his hand and his intent to turn on Hellscream) and agrees to withdraw without bloodshed.