So, I got to thinking about the merging and how the two don't really seem to match in the two movies. How it seems like Dark Alessa was merging with Sharon/Heather twice. But hear me out; what if at the end of the first film one part was still out. I mean, in the movie there were three parts; the original form (Alessa), the evil (Dark Alessa), and the good (Sharon). We were only hinted about the one merging in the first movie. So why is it not possible that at the end of the first film only two parts merged and in the second the third part finally completes it? For all we know Dark and Sharon merged giving Sharon the reason she can snap at someone in the second movie because there is anger. But Alessa is still around and she is still full of hate because the cult is still around. And because it is the original part, she just grows in power giving her all that strength.
That could also be the reason why the two have such different looks as well, one was dark, the other was actually Alessa using her powers to take on a different form.
The two movies don't fit very well together at all. That's because for the first movie, director Christopher Gans pretty much did his own thing, quite a bit different from the games. Then, due to criticism for deviating from the games and the second movie having a different director, the second movie changed a lot to make it more like the games, particularly SH3 (while still making big, unneccessary changes to certain things, like the character of Vincent, it's kind of baffling). Just look at how the cult of the Order is treated in both movies. In the first one they're fanatical witch burners who think Alessa is some kind of antichrist and fear and hate the things in the otherworld. In the second film they're more in line with the games' Order, worshipping pagan gods that are related to the Otherworld and wanting to usher in "paradise" by forcing Heather to birth a god.
It's really not consistent at all. People who went into the second movie without playing the games, having only watched the first movie, must have been totally lost.
So you're free to come up with fanon reasons, but there are far more plot holes than just that. Taken together, the two movies' plots are basically swiss cheese.