It's not so much the killing itself it is how it makes all Ripley's efforts of the previous film to save them pointless.
Then again, Alien: Resurrection made Ripley's self sacrifice at the end of Alien 3 pointless so they got what they deserved.
I can think of several in character reasons why she would have moved slow, or at least slower than we she is capable of, but they could have put a reason on screen. Like being briefed that either by Boy Kavalier that they are still a secret project, or by Kirsh (the synthetic) about the need to...
My main complaint after watching the first two episodes is why doesn't Wendy run?
She finds out what floor her brother is on, and she walks there? She has a super human body, and a kids brain.
The kids I know run everywhere even when they don't need to let alone when there is a reason to get...
I guess you mean sex rather than gender (assuming you are aware of the difference).
But there isn't really a problem with stat bonuses between different sexes of fantasy races assuming they have significant enough sexual dimorphism to be represented by stat bonuses or penalties.
I agree it works really well as a one shot, it is my goto for convention games. Saying that I've played Horror on the Orient Express (1st edition), and Tatters of the King which were both much longer games and it worked out fine. I think the longer campaigns support a slow descent into madness...