Nothing has been announced regarding a holiday show yet but if there is to be a holiday show I imagine we'll hear something soon.
Bye Bye Birdie might be right up your niece's alley. It's a fun show and, if she watches Nickoledoen, she may know who Nolan Funk (Birdie) is. Bye Bye Birdie was my first professional production. Although I was 12 I don't think there's anything in there a 9 year old can't enjoy.
I, recently, ran through the list of what would be suitable for a 9 year old without going to regular Disney route. In the past I've discussed my aunt who has level 4 brain cancer and I wanted to treat her 9 year old to a show in NYC. There are a lot of shows that a 9 year old may appreciate but I wanted to exclude anything that had death in it like West Side Story or South Pacific. I've been watching R&H films since I was in preschool so SP might be good for your niece. It's a beautiful production. I eventually narrowed it down to Marvelous Wonderettes and Bye Bye Birdie. Both shows had their pros but what pushed me to Wonderettes was the fact that I could get front row seats and I thought my cousin might enjoy that.
"All our dreams can come true -- if we have the courage to pursue them." -- Walt Disney
We must have different Gods. My God said "do to others what you would have them do to you". Your God seems to have said "My Way or the Highway".