I don't believe LE has much evidence, circumstantial or otherwise, with regard to Terri's involvement in Kyron's disappearance. I believe it's possible they have uncovered some skeletons in her closet unrelated to Kyron's case, or along the way, such as this sexting nonsense, but that's about it. I'm very skeptical of the veracity of the MFH plot, which IMHO, has helped convict Terri in the court of public opinion. IMHO, if LE had evidence other than the landscaper's word for it, Terri would be in jail. The fact that LE needed a sting to verify the landscaper's claim, tells me they probably only have his word for it, and the fact that Terri has not been arrested, reaffirms that belief.
Dede's interview with People, about LE only wanting to hear about Terri's involvement in Kyron's disappearance, makes me question the circumstances under which the landscaper told his story. Was he pressured? How long was he questioned? Did he retain counsel? Are there outstanding warrants for his arrest? Are there mitigating factors that would create a situation in which his compliance with LE would be helpful to him personally? Did he say she joked about it? Did he joke with her, saying something like, "I'll take care of that SOB for you," and did Terri respond with, "Would you?" Is that the extent of it? Was it serious? Why didn't he report it? Etc...
The questionnaires have always struck me as a desperate plea for help as opposed to a confirmation or reinforcement of something LE already knew, without a doubt, to be true. After hearing whatever evidence the prosecutor brought together, the grand jury, infamous for indicting the ubiquitous ham sandwich, hasn't rushed to an indictment. At least a portion of Terri's alibi checks out. We didn't hear of Dede until after she stayed with Terri, which makes me wonder if LE ever had any evidence there was another person involved, or if Terri's timeline didn't allow her to do this alone thus the need for an accomplice, and in pops Dede, a bit convenient in terms of an extra body to support what amounts to a theory as opposed to a conclusion supported by other evidence, IMHO.
I believe LE knows Dede purchased and/or suggested the batphones, which helped justify their suspicion of her, but I don't think they have anything on her, either. IMHO, Dede is not playing by their rules, purposefully, but for reasons about which I won't speculate in this thread. Also in my very, very, very strong but humble opinion, Dede is a complete red herring.