She was. That was twilight thinking back when she was a filly under personal tutelage of Celestia. In this particular night Twilight caught Celestia off guard. (Celestia used an illusion spell to make herself look slim) Of course Celestia said she ate too much cake.
When Twilight was a filly she woke up from a nightmare one night during a Canterlot Gala. So all the majority off the activity was downstairs. Twilight wandered the castle to a point where she got lost and wandered into the upstairs kitchen. There's where she caught Celestia off guard.
Scoot is Princess Leane which means "Daughter of the Sun" She is a late bloomer and her cutie mark appeared when she was in highschool...along with a horn. Here's she seeks counseling from Twilight who refuses to believe due to her respect towards her teacher, but deep down inside she fears it to be true.