Mia did the easy thing. I still can't believe that. She knows that the ship that leaves without her will be gone for some hundreds of years. She has remained on the planet to die. She will have no other people she can talk to. No shelter save the crude huts. Only the food that she gathers herself.
She could have remained perfectly safe and comfortable as she traveled at light speed. Others could come up with a better cure - they hardly need her for that. And, though this is my interpretation, it was my understanding that the "vote" taken at the planet by the senior staff members was pretty much it - they vote, then when the infection started to spread, they left. They can go back, work on a cure if they choose - or not. They might return some hundreds of years later to cure what remains of the population later - or not. We don't know the politics of this universe, and how likely it was. It's not a wrong decision made by the commader - his loyalty lay to the people directly under his responsibility, but it certainly was the easier one. (Side note: the quote was from Harry Potter, so please don't think that I think that *all* easy choices are "evil" - but I do believe that most "right" choices are the harder ones.)
I am not arguing that the choice to leave was the right one for the rest of the crew - if I was the leader of the team, I might have done the same. At the same time, Mia's choice was still heroic: give up everything in her life, to die among strangers for no other reason than she could. If there are people dying of AIDS, you don't sit back and say "Well, we'll be back when there's a cure - have fun!"
In this case, Mia decided to stay. Perhaps she is a filthy, rotten traitor to the Core for having deserted her post. Fine. But she still made the harder choice, the choice that will involve toil, and possible danger, and possibly even hatred by a people who will only know she took away her disease induced "happiness", and death away from nearly all modern trappings (since now these people will have to rebuild her civilization, depending on how much still works from the original colony's technology, already some centuries old). Is her decision full of "honor", leaving her post? Maybe not - but it is full of compassion to those who are suffering *now*. And for that, this character has my respect, and my appreciation.