So I'd pretty much ignored this program until i saw 'Those old scientists', and ended up binge watching all the episodes.

My opinion of Mariner has changed over time, from initially thinking of her as a military brat who felt forced into starfleet by parents who were starfleet for life, to now thinking of her as a highly (if a bit silly sometimes) competent officer who should be at least a lieutenant, probably a lieutenant commander by now.

So, why I think she isn't. Her friend dying for one, but I also think she knows Riker, so was probably on the Enterprise D at some point. So Wolf 359 maybe? We know she was on DS9, so Dominion war?

She is, in my mind, a broken person, someone who has been thru things that will have broken a lot of people, and have broken her, up to a point.

She reminds me in many ways of Captain Shaw, highly competent, but slightly broken by a past they haven't quite recovered from.