The 21 age restriction is strict. It is only the clubs she would not be able to enter, although I think she may be able to get into the karaoke club. There is still plenty to do and see to keep your daughter amused.
Blue Man Group is worth every cent and more, you should save money buying from our ticket link above.
I dont think it is a place for younger ones in the early hours when the hard and fast club goers frequent. I have been there up to 12.20am with young uns and that was about our limit for minors.