Don't you dare call Ymira useless! She's one of the best companions in the game, with Deshavi and Jeremus. She's level 1, which means she levels really fast and has an int of 11. She's awesome. I personally use her as a tacticion, engineer and trainer. She's also an awesome medic, but since Jeremus starts further down that route and they're in the same "happy group" you're better off making him the medic. You can keep her as a backup medic though. I'd use Marnid instead, he's like Ymira, just a little bit worse. The guys who dislike him are also Lords, which means you can use the lords until you start a new kingdom, then grant them fiefs and recruit Marnid and train him to be a gofer. Shouldn't take long to get him to persuasion 5 atleast.