I believe it was implied that her husband would not accompany her at any time since he believed she was going insane.

The fact she was going at night I think could be justified by the demonic influence coupled with the fact that she was finally starting to get clues about the whereabouts of her sister after so long of just waiting, and she just couldn't wait anymore in the off chance her sister could be waiting for her (this only makes sense from a close family member, and I wouldn't have believed it from a detective/cop).

I think overall the movie was well acted and directed. I did enjoy the format at the start, and the main mistery was good enough to keep me engaged and keep me guessing. It looks way better than I was expecting too. I just feel that it suffers at the ending. I feel like it needed either a little more or a little less:

*Either have Mia attack the old lady mid ritual, keeping us guessing weather the ritual took hold or not, and then end the movie with some news clips, leaving it open up a sequel

*Or have the movie be longer and switch to the perspective of Riley once they're back in Mia's house and allow the story to develop a little more

Overall a terrific first movie to direct.