Nice little horror mystery *MAJOR SPOILERS*
Loved the build-up as they were discovering the clues in the body. Once they got to the end of the mystery and figured out she was a witch, it lost some steam and fell back on some tired supernatural ghost/monster tropes. But overall, very watchable.
My take on the events is this this:
The witch was not all that powerful. She was not making the dead walk, or smoke fill the morgue or any of those other things. She just made the father and son think those things were happening.
In the end, we see that none of the body drawers are open or empty, that all the lighting and morgue equipment is intact, and that there was no storm. It all happened in the minds of the two characters. The only damage we see -- such as the chopped door and the dead girlfriend -- is what they caused while under the witch's influence. I doubt the cat was even injured before the dad broke his neck...just another hallucination from the witch.
Not sure I buy into dad's theory that she was an innocent turned into a witch by the ritual. People with enough power to cut her internal organs and burn her lungs without actually touching her could probably figure out who is a real witch and who isn't one. My thinking is that she was actually a witch and the ritual just didn't work to end her.
Since the ritual failed, she has been lying in wait, trying to find a person to transfer the ritual onto so she can get back on her feet, so to speak. The way she accomplishes this is by playing with her victims' minds. She almost had the dad, but he gave up before the transfer was complete. She lashed out at the son in anger, making him see his father and fall through the railing to his death.
She will just keep manipulating people until she finally succeeds.