As much as I want to agree with you, I would have to go the contrarian route this time and pitch my flag with the theory that Rey is Obi-Wan's granddaughter. He was stuck in Tatooine for a long time, who knows what number of progeny he had produced. With the theory I heard, I was convinced when they pointed out that Alec Guinness' voice was used in that trippy lightsaber sequence at Maz's bar.

It would be too obvious for Rey to have Skywalker blood, and I don't think Abrams would go that direction. UNLESS, he already set everyone up to think too deeply, so now he's going with the obvious path. Really though, why wasn't there a mention of a twin sister? It could be that as you said, the memory has been wiped, but I feel if there was a memory wipe, Luke would've wiped the memory of the twin for everyone. If he really wants to keep her safe, nobody would remember Kylo ever had a twin. Oh my Glob, I'm slowly convincing myself that Rey is Leia's daughter.