I think the reason for Rockford is still a mystery. If she came down to Sterling for Wisconsin Dells the google maps route would have put her right through Rockford in which case she would have doubled back after making the calls. It makes me feel like she went towards Sterling with a purpose, and killing her son doesnt seem like a purpose that would warrant that given, as others have said, there are many remote areas between wisconsin dells and Rockford.
If she were just meandering randomly that might make more sense, but the other patterns seem to support this was thought out.
I agree with you 100%. I think if she was planning on killing herself as well as her son, then why drive all the way back south? Why not just do it in WI? I think that she was planning on meeting someone. I think she wanted to give her son some good last memories before she departed this earth. I think there is a lot more to the relationship that has not yet come out.
Here is a snip:
"Then, when asked about what police termed marital strife, James Pitzen ended the interview. His mother, Linda Pitzen, said James and Amy had no greater issues than any other couple"
http://chicago.cbslocal.com/2011/05/19/search-intensifies-for-missing-aurora-boy/