I think her best shot of getting Kyron out of school would have been to tell him she had to go get some medicine for K. and she wanted him to watch her in the car on the way over (although Andrea from the gym describes Kiara as being with Terri when she saw her at the store). She was allegedly at the first Fred Meyers by 9:12 and the second one between 9:30 and 10:00 am. She may have promised him he would be back at school by the talent show. It would be easiest logistically to then go straight home. The fact that Dede was already at the farm working by 9:00 but they now say they last saw her at 10:30 (and then noticed she was gone after 11:00) could mean that Terri called Dede for help from home and went to pick her up. They were both off the grid at about the same time (or at least Terri's story of driving K. around for an hour and a half cannot be verified). Terri checks in at the gym at 11:40 (although we have no confirmation she was there the entire hour). We don't know who else was at the gym. But that looks to me like Terri wanted part of that time documented.
If I'm not mistaken, the timeline was changed for DDS having been missing from her workplace at 10am.
MOO---It's always been my suspicion that she was a witness, or an accomplice, after the fact.
If Dede had planned on being involved ahead of time, I seriously doubt she would have disappeared from the farm suddenly and missed that lunch. She would have come up with a story or something. This sounds to me like someone who got an emergency call from a friend. Which would not rule out premeditation on Terri's part. She could have easily staged an "accident" and knew she could count on her friend to drop everything and help her out.
Anyone who parked at the back of the lots at the storeslike Terri did may not have wanted someone in the truck to be seen with her. Which could have been Kyron, since Dede was ostensibly at the farm. Although is does not rule out anyone else either.
If I'm not mistaken, the timeline was changed as far as when DDS was missing from her job to 10:00am.
It's always been MOO that she was a witness, or an accomplice, after the fact. For some reason, I don't get that she was in on it from the beginning.
Of course, it's MOO.