Heidi obviously did not think she and the baby were leaving the property. She had taken no provisions for the baby...diapers, formula, etc. She had also not taken any money, licence, no ID of any kind. Only keys and phone! Where would she think she was going that she only needed those two things??
Another thought I had was about the internet searches MF made. I personally made searches on Google for Heidi Broussard for any new information, and inevitably a Web Sleuths comment would be in the results. What if these comments or FB comments were driving her actions in that last week? Maybe she had no plan beyond kidnapping Margo.
Also I think labelling MF as Heidi's bestie is a pretty loose label. I have friends since grade school who are dear old friends, but not my best friend. My best friends live near me, we see each other or talk daily, we go out together. Not a long distance relationship like Heidi and MF had. jmo