She could, but not out of shoelaces, because she doesn’t have any shoes!

Anna stopped imagining options that were not available to her. She had to confront the cold, hard facts: She had kicked off her shoes so she could kick off her panties. When she left the room, she had been so preoccupied with making sure her skirt didn’t split, she completely forgot to put her shoes back on. Honestly, at the time it probably was for the best: if she had bent down to retrieve her shoes, there was a good chance her skirt would have unzipped completely. If she was using both hands to put on her shoes, her skirt would have fallen off in front of all her classmates. She would have no way of stopping them from seeing her pert buttocks and neatly shaved pussy.

Back to facts, she still needed a way to hold her shirt together. The only material she had available right now was her bra. Shoelaces were not an option right now, but they could be if she could make it back to the classroom and get her shoes. However, every second she walked with nothing but a loose piece of fabric around her waist, she risked losing control of it and accidentally exposing herself.