4) She Is A Former Student Of Luke’s
But who says she has to actually be a blood relative of one of the characters and not just have a shared history with them in some way? One less galaxy-shattering theory suggests that Rey was once one of Luke’s students at his Jedi academy. Hence why she shows signs of having had training in using the Force.
In the previously mentioned scene where Rey finds Luke’s lightsaber, Rey has a vision of a young girl witnessing a slaughter courtesy of Kylo Ren at what we can take to be Luke’s school. This is thought to be Rey herself – she escaped Ren’s massacre of the other students and was put on Jakku – either having had her memory wiped or just deciding not to talk about any of this during the movie.
Another part to this theory is that Max Von Sydow’s character, Lor San Tekka, was a figure at the academy who also took refuge on Jakku to watch over Rey, without ever contacting her so as to not give away her position.