Getting this out of the way first? I dislike the fact that we're having this conversation because of some fringe, misogynistic clownshoe like the attention whore over at JTA. That being said...
I was not really familiar with the whole concept of a "Mary Sue". I had to look it up. Yeah. That made me feel old. I eschew the notion that Rey is a "Mary Sue". Notably because the term is usually applied to characters in fan fiction. And I think that's an insult to talented writers like Lawrence Kasdan and J.J. Abrams. As for the questions dredged up by the jta troll?
THE FORCE AWAKENS is very much an origin story. I think Jesse made some valid points about the characters. When it comes to Rey and her arc? First, we've really only seen a small part of her story. There is clearly a lot that remains to be revealed about Reys past as well as her future. What we do know? She's a survivor. Based on the day marks she keeps on the wall of her AT-AT home she has been there for a long time. Her time scavenging the junkyard of Jakku has made her technically adept, and she has to be reasonably streetwise to deal with someone like Unkar Plutt who appears to be the only source for food at the Niima outpost. And he seems content to let her starve.
Based purely on the timeline of the movie? Reys awakening took place some time between her meeting BB-8 and the events on the freighter Eravana. Because it was after Rey, Finn, BB-8, Han Solo and Chewbacca escaped on the Millennium Falcon that Snoke asked Kylo Ren if he had felt the awakening. Rey's ability to navigate her way through the escape from Jakku to the encounter with the gangs and Rathtars on Han Solo's freighter was almost certainly assisted by some Force ability.
And then there are the other pivotal scenes in the awakening. First, Rey sensing the call of the Skywalker lightsaber in Maz's castle dungeon. That plus her Force vision upon touching the hilt were a tremendous step forward in her Force awakening. She saw Cloud City and the burning Jedi Temple along with a mourning Luke Skywalker. I think it's fair to say that she had never been to either place. But where does that vision crossover from vision to flashback? Was Rey present during the rain storm where Kylo Ren ran through the clan leader? I've seen speculation that the clan leader was a protector who was cut down by Kylo Ren and the Knights of Ren, to that same clan leader trying to attack Rey and Kylo Ren stopping that from happening. I think this moment is something we may see revisited and is specific to Rey. Because Kylo Ren seems fixated on finding her when he asked that First Order Officer "What girl?" We also see Rey having a real memory as the starship takes off from Jakku, leaving her with Unkar Plutt. And then the vision moves forward to a premonition as Rey sees the snowy forest of Starkiller base. And during the entire vision she also hears the voices of Luke, Palpatine, Yoda and Obi-Wan Kenobi.
This was not a good moment for Rey. Her reaction is that of someone who's traumatized. Maz recognizes how overwhelmed she is and tries to comfort her. But she's also honest with her and trying to show her a way forward. Rey won't have it. She rejects Maz and runs off into the forest. Then when there are First Order Stormtroopers coming after her? Rey doesn't know what to do at first. But then she fights. Her reaction to her first action on Takodana is notable. Rey is scared. She fumbles with the blaster. And she was initially horrified that she killed that Stormtrooper. But she also realizes quickly that she has to fight or die. But when she encounters Kylo Ren? She's terrified. Especially when he uses his Force abilities to keep her from moving. That is not the reaction of some super-powered, overly idealized character.
The other key awakening moment is the interrogation on Starkiller base. Kylo Ren's probing of Reys thoughts had completely unintended consequences as she turned it back against him. Rey gained insight into Kylo Rens thoughts, along with his fears. Here I think there's some ground for speculation. Did Rey gain all of her insights into the Force from reading Kylo Ren's thoughts? Or did he unlock something that was already there? Is it also possible that she was cut off from the Force, a la Darth Revan, and Kylo Ren unlocked a door? Because right after this she was able to use the Jedi mind trick on the Daniel Craig FO Stormtrooper.
There's also what we've seen in the new trailer. When Luke says something about how he's scared of the raw power he sees? I think he might be talking about Rey. And that raw power may also be why Rey was able to overcome a wounded Kylo Ren at Starkiller base.
Looking through this all? Rey is not a perfect character. And her flaws are there if you know where to look. She's fearful of being abandoned. She has a sense of wanting to belong to something. And she doesn't fully grasp what's happening to her. But she also has some positives: kindness, an ability to work hard, and to stand up and fight even when she's afraid. I think this makes her a fairly well realized character, and far from what the jta misgynist wants to depict her as.