I found a ranger nearby and explained, through my tears, what had happened. He came right over and worked with me on turning, pushing and pulling, and moving the seat forward and back. Finally, we got her worked into a space where we could squeeze her through and she was in my arms, wiggling and licking. One happy puppy!!
I planned to stuff something under that seat so she couldn't get into such a predicament again, but didn't get to it for 24 hours. Yup, you guessed it. She did it again! The next afternoon as I was taking a nap, she crawled under there and got stuck again. This time, she was turned the opposite way, and I could see how she had made her way to the spot she was in, and I simply pulled her by the hind legs back out. I immediately stuffed a blanket under there to prevent a third event.
(The above picture was taken on day two. I didn't stop to take her picture the first time, as I was frantically focused on getting her out. The second time, she had to wait while I got out the camera.)