In Star Wars: The Force Awakens, Rey can't remember why and by whom she was left on Jakku, but she was also very young.
Was her memory wiped? or was she just too young to remember?
She seems to have forgotten everything important; her parents, friends, why she's there, who left her there, everything.
The implication is that she was simply too young to recall anything distinctly. She has some memory of being left, but a combination of the trauma of the event and post-traumatic stress (life on Jakku is hard) seem to have blocked out whatever was left. There's no evidence that her memory has been tampered with.
Absentmindedly, Rey mimicked the mother’s loving gesture, softly stroking the salvage in her hand. Rey had no memory of her parents. She didn’t know why they had taken her to Jakku, or why they had left her there. For all she knew, they were long dead. Yet Rey couldn’t help hoping that one day a transport would arrive and her parents would walk down the ship’s ramp and back into her life.
Notably, a later (also canon) story conflicts with this. She remembers some information about her parent, including their names.
Just a few hours earlier, they dared to think that maybe . . . they’d made it? They’d gotten out of their homestead, their all-purpose house droid, handcrafted from more scrap and salvage, sacrificing itself as it led the hunters astray. Then they found the ship (truth be told, they had long ago earmarked it for such a day—a day they hoped would never come). Launched it, just themselves, a bag of toys and books and a handful of credits, the clothes on their backs. Pointed the navicomputer along a vector that would take them way out of range (so they hoped). And buckled in for the ride.
But now? The ship had barely survived the initial trip. Escaping to Wild Space had been a desperate move, but was far from the endgame. It was supposed to be where they could hide, just for a while, take the time to make a plan and plot a course.
Those options now seemed decidedly more limited as they floated adrift. They’d escaped Jakku, only to . . . what? Die in the cold reaches of space, the old freighter now nothing but a tomb for the three of them, lost forever on the outskirts of the galaxy, their passing unmourned, their names unremembered.
Dathan, Miramir.
Rey.
When Rey was first introduced and kept insisting her parents were coming back, you could tell pretty much everyone was thinking "Uh-huh. Riiiight." Even she seemed half-hearted about it and eventually gave it up. Once she's accepted that her parents weren't coming back, then it's easier to accept the other memory, that they left her with no intention of coming back and never will.
In short, denial. If she refused to accept they weren't coming back, there was no reason to accept the memory they were nobodies her sold her off and left her behind. Once she got over the first hump, then she could accept the latter memory.
