you made a great point about her change in behaviour....
I listened to her ex-husband's audio interview, March...it encompasses alot more than the written narrative. his daughter and Madeline would play a game called Minecraft via Discord platform. they played for several years and was still playing until she 'went missing. Madeline's behaviour changed at some point. she was playing aggressively and was hostile. his daughter complained to him about it and almost stopped playing with her...then...he says, a couple of months ago, his daughter said Madeline was playing nice again with her. which now he realizes coincides with SS having moved out.
reflecting back, he talked about a few times his daughter stayed in that 'effin house' he says (knowing now what happened to Madeline). this is when he lived in Orlando after they split up and before the move to Colorado....he now is freaked how his daughter was unknowingly in danger....he wanted his daughter and Madeline to stay connected, like sisters. and they did up to the point she became 'missing'.
he also mentioned that he would want to talk to JS's mother now at some point to understand why she never liked SS, was it anything specific so he would look out for it in the future. I doubt her mother would share with him why she didnt like him other than he was an unemployed slug. if she suspected 'inappropriateness', it didnt rise obviously to a reportable level, for anyone in Madeline's orbit.
he would ask Madeline how things were going with her mom and SS and HER but she never shared anything with him, and for now, his daughter says the same thing, nothing negative or of concern about SS. obviously, if his daughter does share anything in the future, he says he will contact LE.