If it got bad enough, Usagi was willing to transform again without issue. But she wouldn't be able to carry Garnet out anyways... though a light barrier was not impossible. She was not nearly as balanced as Garnet, unfortunately and nearly toppled over, holding onto Garnet tightly as she almost fell into the fans claws.

"Ah no, but I- but I could make you one!" she didn't know how to drive, but she could get in through the window of the hummer, turn it on and hopefully scare the fans enough to back up. If nothing else, she'd use the car as a place to hide, transform, and get Garnet out with her powers.