I can think of one reason. Misty lied to them in the beginning. Somehow convinced them Haleigh's death was Ron's fault which led to a cover up and the need to keep Misty quiet. Thus, the marriage and the words of praise. As time went on, TN and AS questioned her story and came to the conclusion she lied. Nothing was said until about this time last year. Late July, actually, after Ron was cleared in the DFS investigation. That's when TN brought in Nejame and Tim Miller, and Misty was subjected to a LDT and the hypnosis, LVA, etc. Shortly afterward, Misty took a powder, and before long we heard she and Ron had filed for divorce. There was a notable change in TN's attitude toward Misty, but she had to be careful about what she said because they were all guilty of withholding information. I think she was hoping the whole thing would be forgotten, just go away. Ron should've listened to his mama and stayed away from Misty. But he's a fool. Now that he's apparently agreed to talk, TN can say whatever she wants about Misty.
If Misty were still covering for Ron, I doubt we'd hear TN calling for her public execution. Seems she'd still be singing her praises and feeding her commissary account.