So when we're talking about Mary Sue, it's a matter of degree, and Rey, in comparison to Luke, merely coasts her way through obstacles in The Force Awakens..
Still not what defines a ‘Mary Sue’. You can see that in the examples people have tried to give of canon ‘Sue’s.’
For eg. Someone brought up Wolverine, because he can regen from a single cell. Why did Wolverine need to do that? Oh yeah...he lost a fight with Horde. Really, really badly.
(Although note: his powers weren’t nearly actually what saved him there. His one remaining drop of blood just
conveniently fell in a magic crystal, which is so much better and not Sue-ish because we can ‘explain’ it through the Force being with hi-wait.)
Also, Rey: Got her ass handed to her twice by Kylo, and had to get saved by Finn. Never actually manages to get Luke to train her, is tricked and tortured by Snoke, requires a Kylo-shaped rescue, fails to redeem Kylo, accidentally destroys her/Anakin’s/Luke’s lightsaber, breaks the Falcons gun when trying to take on TIE fighters and ends up having to hide. Which means Han is probably the world’s first non-Jedi Force ghost, for the express purpose of haunting
her.
Oh. Also finds out she’s wasted most of her life and tap- danced with the Dark Side for absolutely nothing, because she’d been in denial and pining for people that never gave a shit about her.
But yeah. Keep trying to convince us that endlessly repeating Mary Sue means something. Despite having pretty much fallen out of use even amongst fanficcers, because it’s became so expansive, subjective, and just generally mean-spirited, that it’s practically useless for actual critique.