I just can't

First off, I am someone who has watched pretty much every horror movie of all kinds since I was 7 years old. It's hard to come across a good horror movie now a days. Mostly I just watch them cause they are easy and you don't have to put too much thought into them.
I've never been scared by a movie before but I have been creeped out by a few, very few.
While watching this movie I felt so uneasy the whole time. It was really well done for the most part, totally believable as a documentary. I was totally sucked in and intruiged to the point where I was late going out with a friend cause I wanted to finish it so bad.

I had to know the end.
It was honestly really great and had an enormous amount of potential (as do most horror movies) then they just had to go and run it into the ground. The last 10-15 minutes are such a pile of horse sh!t that I had to come and talk about it.
Please dear lord tell me why they thought that ending was a good idea??????????????????????????????????????????????
First off the white woman would be tormented - sure, but if anything she would have been solemn with the children around (when they were little).
It's just weird that she would all of a sudden go off after so long and so randomly.
Especially after living peacefully with the dad for like 40 years?
I dunno, I just feel like it came out of nowhere and could have been done a lot better.
I am just so unreasonably disappointed.