I wonder what made Miia so upset

Wondering what could have happened between Miia and Centorea you went to Miias room. You knock on the door but no answer. Inside you hear heavy breathing, it almost sounds like silent whimpering. Concerned you slowly open the door to peek inside. Miia stands infront of her bed with her back to you, sniffing in what looks like a piece of cloth and fiddling with something on the bed. On a closer look you realize it is not a piece of cloth at all, but one of your tshirts, to be exact the one you wore yesterday and the thing she is fiddling with is not on the bed but closer seems to be something in her crotch. Slowly the you realize whats going on and you want to get away hoping she hadn't noticed you yet. You slowly try to close the door but it is to late, Miia turns her head and sees you. She turns bright red in embarrassment and so do you. Miia looks like she is starting to cry and you try to calm her down. You say that its nothing to be embarrassed about and everyone does it.

She sais: “No what I did is not normal at all! I have to show you something Darling, but only if you promise to not hate me after this!”

You promise her you will not hate her nothing could be so embarrassing. You go into her room and close the door.