"Jeff? How did you... How are you so small? And why were you in there?"
Jeff, unaware of what to say, stutters out "I-I don't know! I was sitting on m-my bed, and then suddenly appeared in there!", silently praising himself for his last-minute lie. It was partially true though.
"Alright then... Although, I can't let you run around at this size! You're so small, you could get stepped on! Though, where should I keep you..."
After thinking for a moment, Diana decides that the best course of action would be to just keep him with her, for protection from being stomped. So, she pulls her skirt back up, pulls her panties out along with the waistband of her diaper, and lowers him down.
Diana puts him in, not noticing where exactly she put him. She could feel his rough location, and decided that was good. For Jeff, however, it wasn't as good.
Diana heads off, leaving her skirt to fall back down. Jeff is pinned in her labia, his face right in front of her urethra. "I made a mistake..."
Jeff tries to get out of there, but his movements lower down interfere with her vaginal opening. The movements stimulate Diana, who doesn't know what the feeling is.
Due to her bladder not being fully developed, the stimulation works against Jeff. Without warning, Diana unleashes a torrent of pee in Jeff's face.
When it shot out, Jeff's mouth and nose were flooded with the pee. He immediately tried to cover his face from it, in an attempt to stop it, but his arms were stuck.
After what felt like hours, and the equivalent gallons of pee down his throat and up in his nose, it finally stops. Jeff goes to breathe, only to choke on all of it. The sheer amount he ingested made him feel bloated.
Diana, not knowing what she just did, noticed a slight increase in weight down there, but ignores it.