Though is she the only one? The ponies in the Gala don't count right? She's the only one who plays the cello. Plus, do you know Fiddle? She appears in Nightmare Night and the episode when the apple family raise their barn. I'm not sure if that's Fiddle herself, or that's Octavia in disguise trying to play the violin in different in a different form of genre instead of classical. Also they have the same cutie mark. Though different colors. Just like Doctor Hooves and Colgate. Both have the same cutie marks. I feel like Colgate is the Doctor's Tardis as a pony. Or she could be another Time Lord herself just like the Doctor.
It can go either way, but I'm not sure. I still feel like she is the best Tardis. With that hourglass cutiemark, it can mean that she belongs to the Doctor. Still the other way can go to. Only Lauren Faust knows. She is the one who created her and she probably knows why her cutie mark is the same as the Doctors. I know right, it's weird. O.O We may never know the truth about that mysterious pony dentist.