The difference is your character is not living in a trading outpost with implied off-worlders and already shown speaking multiple languages.

Even looking at the chain of stealing, Rey seems to know the person that stole the ship from Han, as she says his name with familiarity (similar to Teedo).

For this to go against the background presented, it would have to be things that aren’t part of the background presented. Her entire presented background is what’s being labelled as a Mary Sue (good pilot, speaks multiple languages, good with melee weapons, etc.). All of that is established when we first see her: piloting her speeder, speaking multiple languages at and around a trading outpost, fighting with her staff. That is her established background.

Again, it’s far more strange that Finn would be good with a blaster or on a firing squad when he’s a janitor. Even him flying the speeder in the Battle of Crait is suspect based on how quickly it takes place after the film that establishes he doesn’t know how to fly.

But with the woman, we have to tear apart every detail of every frame and waveform to complain that she’s a Mary Sue. It just doesn’t make sense to me, these films have bigger issues and this “issue” was addressed in the original films, as released.