I haven't talked to DD#2 yet, she's at work, but this really made me go "hmmmm"

I parked my car in the driveway Friday after work. DD#2 came home shortly after and we did some chores, cooked dinner, watched TV then both went to bed after 10:00.
Saturday we went grocery shopping (used DD#2's car.) I did some yard work in the front and my car was clearly in the driveway. DD#2 mowed the lawn, did some laundry, then BFbob came over, visited for a while and when he left DD#2 went to visit some friends. I watched them both leave, DD#2 in her car and BFbob in his car.
DD#2 came home with a few friends. We cooked dinner and a good time was had by all. Friends left by 9:00 since DD#2 had work this morning. DD#2 went to bed and I stayed up for a couple hours watching TV.
I mention the above because I honestly cannot think of a time when DD#2 left the house without my knowledge.
This morning, Sunday, I had a breakfast date. I was running short on time, also knowing that I needed to stop for gas, and I could not find my keys. Anywhere. Frantic search, retracing my steps, checking pockets, etc. Nope. No keys.
I grabbed my extra set of car keys, called my friend to apologize/explain why I might be a few minutes late, ran to my car thinking I'd stop at the gas station for just a couple of gallons in order to get me there and I'd fill up later.
I start my car.
My gas tank is full.
Hmmmmm . . . I'm wondering why on Earth would DD#2 take my car when she has a perfectly good car of her own . . . Why would she fill the gas tank . . . and, especially, where are my keys?