EDIT - Originally said "Kill yourself" but that's a bit harsh. But saying an argument and ending with "ugh" is fucking tumblr-tier.
I got the mary sue vibe as well, but only initially in the moment when Finn meets her - as a character she's flawed; as flawed as Luke was in the OG trilogy. Kenzo's right, if she's considered a mary sue, he's definitely a gary stu. I thought she was really well done. None of that cringe-worthy YEAH, GIRL POWER! we see in shows like Supergirl or from what I've heard about the newer Mad Max.
Also what the hell is with that guy's hair? Did he cut it himself?