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I don't particularly have a guess, since PT is the only anime I know of with ballet, but others might be able to help you out if you can remember like, what the girl looked like or what she was wearing? Or if she was dancing by herself vs in front of an audience, etc.
Kaleido Star?
It's pretty obscure so I don't know if it'd be on On Demand, but could it have been Puchi Puri Yuushi? https://youtu.be/jtmBTaxQPi0?t=19m32s
This anime was on Time Warner Cable's anime on demand service years ago. The episode had a scene of a girl doing ballet or some other dance. It's not Princess Tutu