I'm not so sure that TA was at the car ambush site. The plan was to bring the children to Four Corners or wherever the meeting point would be. She would have had to "keep up appearances" and show up, or at the least feign some excuse. But the children were with her, and they are old enough to answer questions, regardless if they were coached to lie or not. LE has experts in questioning young children. If they weren't with grandma during that time, that would be a major red flag. I wonder if TA actually called VB "we're waiting, where are you?" or some such in order to cover herself.
However, if she's <modsnip - no link provided>, and having influence and being in control of the local LE maybe she did leave the kids at home and participated in the actual ambush and killing.