Lena possibly moved away from her mother to start over. Jeanne Decker, Lena's younger sister, wrote in a statement to The Salem News that before she disappeared, Lena had planned on moving to Arkansas with her son Colter, as she had been with the wrong crowds and wanted to start over. E.J. Schulke, a former neighbour, also recalled Lena talking about plans to save up and move to St. Louis.
This theory hasn't been ruled out, but it's still highly suspicious that Lena did not take her son Colter and has not reached out to him in any way.