SPOILERS If she was the mother...
SPOILERS
Ok, I guess the most plausible explanation (so far) is that she's the real mother who had just came back from a plastic surgery and suffers from depression after the loss of a son and her divorce.
Elias is clearly schizophrenic (or a psycopath?), kills his mother and maybe had also something to do with his brother's death.
If that's true, who the hell was that girl on a picture with their mother, dressing exactly like her?? She claims it's a "friend", but I guess there's more to it.
Any help??