The 'Decatur phone ping': if it is an accurate report, that it was ET's phone, it might suggest one of two things:
1. ET was beginning to get anxious, and attempted to use her phone, or
2. ET was instructed to turn on her phone, and then turn it off. And they would back-track, and head in a different direction. I agree with SouthernCutie & TNHybrid - the 'ping' just might be a Red Herring.
Destination: I lived in Nashville, and traveled to/through the Great Smokeys, and on to Gatlinburg. A person can definitely disappear there. As long as they are not seen together, they can disappear for a long time. Until one of them, is overly confident, and slips up.
Marriage status updated as wife: I am not surprised. As I continue to write down quotes of his statements about her (father figure, etc.), it suggests that 'only he, knows what's best for her, only he can bring her to church, and 'save her', etc. In short - he is 'the only one' for her. If he can convince her that he can marry her, he can convince her that they can live as 'husband and wife'. And all that goes with that.
OnLine Marriage 'certificate': I am wondering, if there are 'online pastors', who can perform 'paper marriages'. Legal? Hell no. But TC could easily convince ET that it is.