I'm going to write a bunch of stuff here at the beginning so that if you use the app like I do, even if it says 'Spoilers' it still shows the title of the review and the first few lines of the comments. So if the big reveal is mentioned right away then say goodbye to enjoying the movie.
So, to me, this movie gave away the ending from the title of the movie. The Lie. Not Lies, not Cover-up, not Responsible, nor any other title that could have been chosen. The Lie. So there is one lie. What could it possibly be? Duh. She lied about the whole thing. I suspected from the very start and was positive when the mom woke from a dream of seeing the supposed dead girl. Not to mention the absurdity of the girls' plan. Other spoiler reviews go into depth concerning the absurdity so if you're curious, read those. My point is that with a different title, some more realistic clues, and a little more intelligence given to the character of the lawyer mother, this could have been a decent movie.