My opinion of J.J. Abrams ability to make a movie has jumped light years. Not only has he made in The Force Awakens a great movie, he has had the world wondering about who Rey is and her heritage. The silly thing is, he has already told us and in Luke Skywalker's (Mark Hamill's) own words. We just got so caught up in the movie, that we totally forgot the trailers that we watched with great anticipation months before the movie was released.
In Trailer #2. https://www.youtube.com/watch?v=ngElkyQ6Rhs The force is strong in my family. Luke says "The force is strong in my family. My father has it. I have it. My sister has it. You have that power too." Now I suppose the argument could be made that he was talking to Ben Solo a/k/a Kylo Ren but if he was I believe instead of saying My sister has it, he would have said your mother has it.
No, J.J. Abrams told us that Rey was Luke's daughter but for some reason he cut that out of the end of the movie and left us hanging. It is okay though because he had already told us in the trailer, we just forgot about it. So all the silly theories about being a descendent of Ben Kenobi or Anakin Skywalker reincarnated were already debunked before the movie was even released.