[@ihinka] Awesome :)

okay so

1. They would still be officially at war, but it isn't a very active war, since Mar is a lot more focused on the Free Isle and they're mostly ignoring the Isle, which is happy to be ignored. though, Mar is still a threat they try and stay prepared for at all times.

2. I would say they're a sort of western - european type country along with most of arrylia and mar, and that chorn, endeny & kopan are more asia-based. Yeah, in Arrylia it would mostly be the four fluids ideas of medicine, leeches, and just starting more experimentation with herbs and such. 
Chorn would be the most medicinally advanced of any country. Acupuncture, herbalism, more knowledge about stages of illness and diagnoses. the best of the best would learn the stuff here, yeah, but Endeny copies from them a lot, so it woudl be a close second. 

3. If they were taken as slaves, it would likely have been from a Chartan raid, where you would get that type of environment. The samurai type people are from Endeny, where the issue is slavery is also legal. If they were to attack the ship, they would keep the slaves themselves. Possibly, she could escape and set herself adrift, only to be picked up by Endenic missionaries/monks? That would be my suggestion, but it could be merchants, or perhaps if an Endenic ship attacked them, she could have convinced them she was hired and not a slave, or perhaps the captain may be racist and feel pity for her because she was from Arrylia, not Charta, and a girl. I would suggest that maybe she made her way, was rescued by people from, or was dropped off at, the East Island monasteries where she could get the sort of training you want.

4. I think Cold has a good idea for that. Perhaps she is defending her home, if she set up shop in Chariot and wants to keep her life there. Perhaps she has a family living there now? Or even just friends she cares for and a lifestyle. 
She may know Avoir personally and agree to help him defend the Free Isle. He may have asked her to go along with the crew as a healer to help them in their missions, which while sometimes will include combat will often have the option of diplomatic choices. (and sometimes you might not be fighting humans anyway). 
I was thinking that when they land in Arrylia, she could be there to meet them. She could be Amia's contact through Avoir who wasn't in the Free Isles at the time of recruitment, but had agreed to help since she was already in Arrylia for whatever reason (on business, or perhaps: the destination isn't far from the Reflection Isles - she could have visited her mother or something.). Then she could proceed to join the party for the mission and choose to continue on the next ones.