In all honesty, Marissa sounds like a very disorganized person. When I read her blog post, I wondered why her son was barefoot in his carseat on the way to school anyway - wouldn't you want to put the shoes on the kid before taking him to the car so you're not stuck doing it in the parking lot? If you know he's going to school, why not get him all ready?
And then she says she was barefoot in the parking lot because she left her shoes in the car - so she was driving barefoot? She knew she was going to get out of the car to gather her kid, finish dressing the kid and presumably walk him into school yet she didn't put her shoes on? Honestly, I could see how other mothers might judge her if she was dressed in her pajamas, in yesterday's makeup, barefoot and struggling to finish dressing her son in the parking lot (since she admitted she always dresses like that and it wasn't a one time, I was so frazzled thing). I get the feeling that that probably happens often since Marissa doesn't seem to have any morning routine - if she's constantly stressed and frazzled and throwing things together every morning, she probably was rude to the other mom.