But... How would she know the moment the gasses reaches her vicinity?
Like I've said, they aren't slow gasses by any means, and I recall speed equalisation excluding attack speed statistics from the equalisation equations. And since you've said that her universe has nothing similar to the gasses that Mercer did, I don't think she would immediately assume he is inhuman just from gasses appearing. She could likely assume he has some kind of hidden equipment or device that discharge such gasses for all she knows, and she could also assume that it's a smokescreen rather than tear gasses. Then again, I don't think gasses travel as fast as the ones Mercer unleashes, so I'll give you that. I'm not sure if her stalling does anything, but okay then.
I mean, unless the OP decides to change the starting distance now, we're basically stuck with the one the OP listed. And as Lucy actually has a win-condition that she does in-character (it requires her to go full nuclear straight away though, and would need the blast to directly encompass Mercer's entire body to atomize him), this match isn't quite a stomp, even if the odds are a bit stacked in Mercer's favour. Not like I can make it more fair though, because I'm not the one who made this thread.
I mean, there is Dana for Mercer... And there is Kouta for Lucy... Granted, I'm not sure if they absolutely don't fear Mercer and Lucy respectively though. Is similar experiences the only thing they have going for each other for the ship, rather than their personalities and philosophies compared to each other as well?