Interesting theory. Plausible. But I don't think so.
I think it's probably going out of it's way to try to make sense of a plot that doesn't make sense. It does tie it all together, but it's about as much of a stretch as trying to make a coherent plot out of VII and VIII.
Does Qi'ra have any Force sensitivity? It claims ties to the Dark Side but that's only a business relationship as far as I remember. If neither of Rey's parents seem to be Force sensitive, they haven't really gained anything other than being a half-brother to Kylo. Which is what they use to try to tie the two together like Luke and Leia. But Luke and Leia had a Jedi/Sith for a father so that's why they are both Force sensitive and have a connection. It would be another stretch.
The part about how Leia treats Rey in VII is plausible but it's far from the only explanation. Han's treatment is more circumstantial than anything. I think they both would have acted differently in trying to protect her if they knew who's daughter she was. If she is Han's daughter that he doesn't know about, wouldn't their be much more of a reaction? If he does know about her, why was she just left there? And why is is so shocked to re-discover the Falcon if he knew it was there. Not working.
Finally - and mostly - it has been spoken about several times that Episode XI will be the "End of they Skywalker saga". Assuming that's true, that only leaves two options. Either Rey isn't Leia's daughter or she dies in the film. The latter would seem to be a waste of the supposed storylines in VII and VIII. The former would mean the theory is wrong.
Sell