Calm is what Rarity would call the start of her day, she got up, freshened up and got ready for the day. Twilight had already gone somewhere early in the morning, so Rarity had the whole castle for herself till her gf came back.
She smiled, making herself some coffee and breathing in the scent and enjoying the silent chirping of birds outside the widow behind her.
She went to a room Twilight prepared so Rarity can create her dresses in peace while staying at the castle, grabbed her Gems, gems and more gems! book and started searching for
gems to use in her new design.
That is, she would have done that, had twilight not burst into her room giggling and jumping.
''Ah, twilight! Where have you been?''
''AJ held a pet tournament for everyone to show of their pets and RARITY there was a book shaped ball! AND IT BOUNCED! so I did what every princess does, I kindly damaged they give me the ball, of course I gave them some bits in return BUT I HAVE THE BOOK BALL RARITY!''
Twilight shoved the book ball to rarity and started jumping
''see! isn't it amazing!?''
Rarity rolled her eyes, then stopped and smirked.
''Hey Twiiliiight~'' she sang as she wiggled the..Bool? Lets call it bool. As she wiggled the Bool in front of Twilight.
Twilight's eye practically shone as she got down and started wagging her tail
''BOOK! Rarity throw the book!''
Rarity did as Twilight asked, and threw the Bool through he door down the hallway, and Twilight ran after it.
''And to think I debated adopting a dog..'' Rarity asked herself as she watched Twilight face-plant the floor running too fast and trying to stop, to pick up the toy.
''One is enough..''

I think Werewolf twi AU is, probably one of my favourite AU's, for multiple reasons, and twilight acting like an overgrown puppy is probably one of them.