Let’s go with the bra idea. What’s the worst that could happen? (It works, for now)

She decided her best option at this point was to make a belt out of her bra. She was going to have to get stark naked in the library for a while, but she would just have to deal with it. She looked around, slipped off her shirt and unhooked her bra, then put her shirt back on.

As she fiddled with the bra, she realized she did not have any tools for the job. All she could do was carefully tear it apart with her hands and hope it did not become too mangled to be usable. In the end, she succeeded in removing enough elastic to fit around her waist. She threaded it through her skirt’s belt loops and clasped it at the back, around where her zipper used to be. The difference was, it did not hold the rear shut. She would just have to walk carefully.