Don't you find it a little odd that Rey was left in Unkar's hands when she was a little girl? You can clearly hear him and see his hand grab hers in her flashback. I dont think it is too crazy to think that the Falcon was left behind for her or could have been some form of payment to Unkar to watch over Rey. If you notice Hans reaction when she says she is from Jakku, he obviously realizes who she is then. He even tries to keep her with him by offering her a "job" on the Falcon. He has some vested interest in her. If she is his daughter maybe he didnt want here knowing just to keep her safe. I mean if you dump your daughter on a desert planet to hide her form Kylo, or the New Order, you sure aren't going to come right out about it to her and push her right back into the spot light. Although she is doing a pretty good job of that herself. Plus you cant overlook the reaction Kylo has when he is told that Fin escaped with the help of "a girl". He obviously knows a bit about her history too. He didn't even flinch when she showed up with Luke's saber and immediately says "that belongs to me." Wouldn't someone that had no clue who she was wonder how she acquired it? I dont think EvanDickson theory is too far fetched.