Actually it almost certainly is not possible, given the school records show her in at 7:54 and out at 10:50. The tiny window of opportunity, the fact that the school would have noticed her missing, the blood, the weight of the body all make it extremely unlikely. Ali strikes me as someone who has been through a lot (and had a lot of therapy) and is probably naturally a bit off (given her childhood and mental health issues) but to go from that to "yep, she murdered her mom" is a massive leap. My wife was convinced it was her as well until the last episode finally shut her up.
So good sc