I do think the Gram is maligning this search with her BS, but I do not believe for a second that she would help Casey with a ruse if she knew she killed Kaylee. There is no possibility she would let that child be "out there" (being sensitive) indefinately. The most telling thing I heard her say was something like "people have to process these things in their own way"
when asked why she can't get a straight answer out of her kid. That speaks volumes to me. She may not be willing to admit to her herself yet, but she knows already.
Remember, she left the house, went back when they were away, shed was locked- this girl had a substance abuse problem, period.