This one was surprisingly good. Its revealed right away that Ma is disturbed. Parts of the film reveal a backstory to her character from a past trauma from high school involving a couple of the main teens parents. Her loneliness makes her become attached to the teens in this film and then turns ugly when they reject her.
These kind of films usually use a young antagonist for the part, just this one went a different way and used a grown adult. The violence towards the end was pretty disturbing. Some of the deaths are towards the last half of the film. I was just expecting a larger and more intense showdown at the end, but it was pretty brief.