She's willing to help her friend out

"Don't worry, I understand. I can help you. Can you tell me where your other supplies are?" Marinette asked in a very soft tone of voice.

Mylene nodded and took out her backpack, which had a changing mat, some powder, and a couple more of her dia--protection.

Marinette made sure nobody was looking, and then took Mylene into the bathroom before locking the door. Meanwhile, Mylene was nervously taking off her pajama pants. She was always a very timid person, but she felt like an actual child, especially since she knew what Marinette was going to do next. After Marinette took out the changing mat, Mylene laid down, letting out a nervous squeak as Marinette slid off her panties. Taking out the container of baby powder, Marinette started to gently sprinkle some onto Mylene's rear and softly rubbed it in. Being a babysitter, Marinette was used to this.

Marinette then unfolded the garment that Mylene refused to say the name of and slid underneath her. She pulled up the front and soon fastened the tapes over her waist. "There. How does that feel?" She asked.

Mylene's face was bright red from what just happened, but she was still grateful Marinette did this for her. "Th-Thank you..."