I don't have a link but there have been several articles in the Southern Standard, the McMinnville paper. One of them was a regular feature in the Sunday paper called Business Pulse. The reporter does a lot of opinions in that column and post partum depression was mentioned.
Maybe the motive has not been at least hinted at because the cops don't believe it? Withholding this kind of information unfortunately generally leads to wild speculation. Her lawyer made some incredibly stupid comments about women in this country being second class citizens, possibly setting the stage for an abuse defense. A neighbor said the husband was aggressive and they had an argument over a dog.
An interview with the TBI spokesperson (I think) said that they found evidence in the van and where they were staying.