Something that my wife and I noticed after hearing her quote that her parentage should be obvious is her accent. John Boyega and Daisy Ridley are both English yet only Finn has an American accent. I doubt this wasn't intentional and if her parents dropped her off on Jakku at age 4 or 5 and was taken into care by Unkar then where would she have developed her English accent? Leiah, Han, and Luke all have American accents so maybe this very subtle hint was the obvious thing she was talking about.
Also not sure if this has been posted anywhere else but after digging into the subject even more it looked like there was some pretty hardcore and convincing research into the Obi-Wan as her grandfather theory done by the Huffington Post:
http://m.huffpost.com/us/entry/8911656
It pretty much lays out how essential the relationship of Obi-wan to Anakin and Luke trickles down to Kylo and Rey. If she is his granddaughter then her being able to "save" Kylo from himself the way Obi-wan couldn't with Anakin would be why thematically it would be cool for Obi-wan to be her grandfather.
Not only that but it adds much more to the light saber scene when she finds it as Maz's. It called out to her since it was her job to delivery it to Luke, just how Obi-wan had done the same in ANH. The final voice in her vision of Ewan Mcgregoe saying "these are your first steps" also is telling.
Finally, if her true calling in the movie is to deliver Luke's light saber and motivate him to come back to fix things, then the stare down finale has more weight since Luke possibly did train her as a child but had to force erase her memory. So seeing Rey, whom he still sees as this young child who he had gone out of his way to protect, a relative of his mentor, to get her away from the knights of Ren, only to show up and deliver his light saber... it's just wow. Kinda like... "why did it have to be you." Or maybe a "the force isn't done with me yet" sorta thing.
All in all it's super fun to guess and just play around with the idea even if it ends up being something obvious like she's Luke's daughter.