I do think it might have been hard to present marshall as the leader or main character if hes got a supporting character who was both smarter and tougher than he was. I mean, I know shes only tiugher because she survived a year alone in the lost hour and kind of had to be just to get by, but thats essentially a years more experiance than marshall has, and in a much more hands on way.

in comparison, with simon being so much younger n dash being in many ways a 'lost' character, as well as having the whole shades of grey morality, its easier to establish mars as the central character with that dynamic.

it is a shame we never got to see her again - maybe they were all intended to come back later on and cancellation is the only reason we never got to see it.