Original description:

Bon Bon was home, in a house she and Lyra shared. She needed to take a bath after a long day of working, making candies and such, so she went into the only bathroom and locked the door. She took her time preparing a relaxing bubble bath with a rubber duck.
Just as she immersed herself into the warm water, somepony started knocking the bathroom door. It was her unicorn roomate, telling her to open the door, saying how "badly she needed to use the little potty".

But the sound of hind hooves dancing and hitting the ground while the front hooves of the lyrist moved from her crotch to the door and back wasn't going to prevent the earth pony from enjoying a long, long bath...

And Lyra was stuck there, doing a human-like potty dance, not wanting to use another bathroom. Will she be able to hold it? Or will she helplessly wet her pullups? You decide.

So, yeah, I'm into pee desperation-omorashi too.