THANKS SO MUCH to everyone who replied!!!!
Sometimes I just need to see and read the words of what my gut is telling me
I ended up texting her that night saying simply "Carpooling is stressing me out and hurting our friendship. Let's take a break and just take and pick up our own kids." (I knew that short notice would not cause a problem for her.)
Saw her the next day at dd's game and we looked at each other and just said 'sorry!'.
Things feel ok. I feel WAYYYYYYY less stressed!!
PS: Writing here for help really saved me from going off the deep end and binging my brains out! While I DID eat more than usual, I only ate foods that are on my plan (cheese sticks, ff cottage cheese, greek yogurt). My new 'comfort foods'????