New here. Great insights by all.
My thoughts:
I feel the clothes were packed because it was a Friday and she had plans to hang out with friends. If she had intentions of showering at the friend's home, then i'm sure she would want to put on fresh underclothes too and not the same ones she had on all day in school. That to me, says why the shoes weren't found, because she was going to wear them and only change the clothes.
As for the makeup and brush, her hair appeared to be curled in the photo taken that morning. Maybe she didn't want to brush the curls out and didn't take one. Her eye makeup was done and if all she needed was a lipstick/lip gloss, she could have carried that in her pocket.
I feel she knew who was in the car. If it was a stranger then the car would have to be close by and pulled up as soon as she reached the end of the driveway. I'm leaning more to her knowing the person driving or whoever else was in the car. I feel she was told she would be given a ride to school and when the vehicle wasn't going in that direction, she attempted to use her phone, and it was taken from her and tossed. I don't want to think what may have happened to her after that, but i think the purse was ditched later when no one was around.
I think there are people who know exactly what happened but don't want to rat on anyone.
I hope my hunches are wrong and she ran away and will return or be found safe.