Cloudy Mist (Who would be Shatter in the future) just lost her parents and the days following her parent's death, she neglected her needs, which meant that she rarely ever gotten out of bed unless to use the bathroom. Here she made a mistake of rejecting a Chamber pot and she indirectly went nearly 10 hours without going to the bathroom, making her unable to move so she had to call for assistance who brought a Chamber Pot into her room and helped her out of bed. Once placed on it, she instantly empties her bladder. This here was when she discovered that she liked it but didn't know that this was a fetish, she would learn this a few years later.

And yes, I sort of implied a fetish onto a child but this is as far as I would get since a foal having sex or their genitals displayed would be foalcon. So it's safe to say that this isn't in that territory.

Disclaimer: MLP and Transformers belongs to Hasbro.