One is that Octavia wears diapers and acts like a baby as a way to relieve tension or at least escape from her hard home life, with either Stolas or an OC finding out and playing along with her.
Another idea is that due to her age, Octavia is still technically a toddler who isn't potty trained yet while trying to prove she isn't a complete baby to her father like in this picture (
https://www.furaffinity.net/view/36924570/)
And this is a little cliched, but I thought of one where Octavia is diapered through a curse of some kind. Not sure about that one, but I'm open to suggestions.
Do you have any other ideas?