If I see my sister at 5:30 pm and she doesn't text me in the evening and I know she has to work all day the next day, I wouldn't be surprised to not receive a text until the next evening. Same thing if it were my friend or even my boyfriend (especially if I saw that snap at 10pm) If it were my daughter and she didn't say 'I'll be over after my jog' instead of just 'ok'. I wouldn't think she necessarily thought brats were a great idea that night. I may think 'huh, I thought she was coming' but if it's basically a standing invite I'm not sure I'd dwell on it. (Also, no one knows what time the mom leaves for work, maybe before Mollie, so if the car was still there in the morning why would that matter?)
Now, if all her family and friends got together at say 11pm and said - no one has heard from Mollie since 7:30 that MAY throw up red flags. Barring that, isn't that just a typical evening? They all thought she was going to work at 6:30 then the fair - I bet no one expected to hear from her necessarily.
So it's not shocking that no one heard from her in my opinion. Until work called DJ around noon?