First, a short detour

As Mary and Serena led Julie to her next class, Mary looked at Julie's shorts and got an idea...

"Oh my gosh, Julie! Your shorts are coming apart!" Mary practically yelled for everyone to hear.

Mary winked at Serena, who quickly agreed and the two urgently pushed her towards a girl's restroom. They two had to suppress giggles as they knew there was nothing wrong with her shorts.

"What is it? Did it rip open? I don't feel anything." Julie said, trying to look behind her.

"Don't try to strain yourself. You can see it without a mirror. There a hole right where your butt meets the back of your legs. Right in the middle. If you sat down, it could just burst wide open." Mary explained.

"Yeah, we need to get you a replacement." Serena said, nodding to Mary.

Mary unbuttoned the denim shorts and pulled them down Mary's legs.

"Eeeek!" Julie screamed, covering her bare crotch, blushing.

"Oh don't be so modest. We saw all of your body earlier. Anyways, we gotta go find something for you to wear. I know! I'll get my gym shorts." Mary said.

"Wait, can I look at my shorts?" Julie asked.

However. Mary ran out the door, leaving her bottomless with Serena.

"Don't worry, she'll be back in no time. Can't be late for class!" She assured her half naked 'friend'.

Julie hid in a stall until Mary returned.

"Hey, I got the shorts, whereis Julie?" Mary asked as she gestured to Serena to get closer.

"Oh, she's in that stall just in case anyone else entered." Serena Saud, looking at what Mary was showing her.

Mary held the shorts up and pulled the drawstring out. Now they would be much looser and liable to fall. Given they were pretty baggy to begin with, it wouldn't be difficult for them to fall off and Julie be none the wiser, at least for a bit.

Julie exited the stall and saw the shorts. Mary helped her push them on and made it seem like they fit just fine. Julie sighed in relief and followed them out into the hallway. Serena and Mary then took her hands and led her to her class.