"Wow! You somehow went back to when you were a baby?!" Celestia cried in surprise.
"Yeah, pretty crazy, huh? That was when I woke up and found myself back in my adult body but all diapered up." Twilight explained as she blinked, hearing her voice was much like her much deeper adult tone. She then looked down and saw she was now much taller, towering over baby Trixie, who was babbling and cooing at her, seeming to be angry that she was out of diapers.
Then it hit Twilight! She and Trixie had been talking in baby babble the entire time. How could Celestia know what they were saying? Twilight turned towards Celestia and asked. "Wait, you can understand, baby babble?"
"Of course, you pick up on a lot of things over the years," Celestia snickered as she trotted over and hugged Twilight, wrapping her tightly with her wings as she said, "As much as I love babying you, I'm glad you're all grown up now. Maybe you'll stay that way this time."
Twilight couldn't help but nuzzle her back, loving how much of a connection the two had now that Celestia had nursed her and changed her diapers. It was odd, but the princess seemed to see Twilight was almost like her daughter.
Twilight then looked around the room and asked. "So.. you'll keep this nursery…just in case I accidentally turn into a baby again."
"Of course! Never know if you'll go back to diapers," The princess chimed. "Or there may be other side effects to your transformation that might affect your potty training. Who knows?"
"Hopefully, that won't be any time soon, but thanks all the same!" Twilight cried before flying off, still somewhat embarrassed about the whole situation and wanting to leave as soon as possible.
Meanwhile, Celestia just sat back with a smile, secretly hoping Twilight would somehow turn back into a baby soon and maybe for a much more prolonged period of time. Maybe for long enough to get to experience Twilight's toddler years. Possibly Twilight would be easier to potty train than Luna or Cadence had been?