So, with the scavenging, she was by all accounts at the bottom of the pole in terms of social class if she was allowed to be so easily screwed out of her portions like she was and couldn't do anything about it. She didn't beat that conflict except by stealing the Falcon from her boss, and she did that unwillingly, and I am pretty sure it wasn't all that great a loss to him. She escaped the storm troopers, but it has to be noted that she only did so because Finn was an extraordinarily good shot and would have been dead without him on the guns. She didn't 'win' the freighter incident, she just survived it, with her greatest victory being that she could close the doors on the monster in time so that Finn wouldn't be eaten. Otherwise, all she could do was get in the falcon and GTFO with Han (though she admittedly helped by pointing out the compression issue, but even then, Han would have spotted that a second later). She flat out lost in the storm trooper invasion on the rebel base, and the few victories she did get were against stormtroopers, and those weren't well placed shots. That's one thing Rey is undoubtedly less talented in than any other fighter, she flat out sucks at blasters. Not to the point that she can't take down stormtroopers, but you should pay attention to the wild shots she is taking when Kylo Ren stomps in. Then she won the mind battle, and successfully sneaked about, lost and wandering, until Han and Finn spotted her. Otherwise, what would she have done exactly? Ren suspected that she'd steal a ship, so he immediately ordered to put the harbors on lock down, so she was screwed there. She couldn't do anything to save Han. She was on the run for most of the fight with Kylo Ren (i'll get into the particulars of that fight in a moment) and then found a ship to steal away from the base afterwards.
She definitely has some wins in there and she isn't utterly helpless in any of them. But this does not seem like an overwhelming win chart to me. She's always good enough to get by, but the fact is that she's subject to the forces that move the world. She can't just take over that colony or whatever she's at in the beginning, she had no recourse except to GTFO against the tentacle monsters, and she didn't fight back the whole base when she was running around. She can't take on the world.
What about internal problems though? Well, other than when Kylo Ren is trying to get at her, she's her own worst enemy. The internal drama that drives her character arc is the fact that she can't let go of Jakku, which she actually hates, but that's where she believes her family will come for her. And this actually prevents her from doing what she wants. This is most obvious after the freighter incident. At first, she was getting away from Jakku for personal safety, but then they actually get away, and she is simply stunned by the forest planet they find. And then they get out, and Han offers her a job. This might be the most giddy she gets, and that's important. You can see she wants to do this so badly. And then you see her crest-fallen. She can't. She needs to go back to wait for her family that she knows she is never going to come back.
Like I said, flaw is a subjective word. It's not as bad a term as Mary Sue, but I still feel asking what Rey's conflict is more applicable than asking what her flaw is. But, gun to my head? If I had to give if a definition, "flaw" in narrative typically denotes a character aspect that prevents a character from achieving what they want. Her flaw is her inability to let go of the past and embrace the new life she has set before her. Han offers her a job, and she runs away. She feels the connection with the lightsaber, and she runs away. She is plagued by self inflicted loneliness. You can see her harshly try to turn away any allies, from BB-8 to Han to Finn helping her out, trying to keep an emphasis of self reliance. Her character journey is coming to the decision of moving on, and embracing her connection with the force, which is done as of the end of the movie. Perhaps that's why some people feel she has no flaws. Because by the end, the focal character drama she has is resolved. Which, of course, doesn't mean it's gone. We can fully expect that her family will play a part in the future movies. But she now has a new path in life, and she embraces (literally) Finn as an undyingly loyal friend and comrade. Her loneliness and attachment to her past life have been alleviated and her 'flaw' has been dealt with for the nonce.
Still, regarding the external challenges she faces once again, some people feel she gets off too easy. I will admit, those ship maneuvers are pretty impressive for someone who has never gone off world, and she is a pretty quick study with the force. So lets look at some of her conflicts a little more in depth.
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People have called Rey's use of force a cheap power up, and I don't think I can disagree about anything except the cheap part. That's what the force is, an empowering aspect of the universe. Luke was empowered by it not because he 'mastered' it, but because he let it flow through him. His mastery of the force under Yoda's training is never about him controlling the force, but flowing with it. You don't get strong ON the force, you get strong WITH the force. And as I mentioned, Rey simply doesn't have the kind of hangups Luke had about the force because she has a different perspective on the whole thing that gives her an arguably easier time accessing it once she accepts it into her life (which incidentally was a problem Luke never had).