I think she's responsible, though I have no clue what his fate has been, poor child. Watching Kaine, TY and DY, likeable or not, they all come across as grieving, angry parents and step-parents. TH is the only one who does not. Her behavior directly after the loss of her step-son and biological daughter and husband is so skewed from normal behavior, I personally suspect she isn't psychologically "normal".
That leaves me with a psychologically troubled woman being the last person in the presence of a missing child. So yes, I suspect her.