What sort of performing arts? Acting? Singing?
There are some local choral groups & instrumental groups in the area that have concerts & are also open for the public to audition. We have a couple recent threads about that, so you can do a search for them.
For opera, there are some companies that put on a couple performances a year.
Opera Company of North Carolina
http://www.operanc.com/
Long Leaf Opera Festival (takes place in June)
http://www.longleafopera.org/
Durham Savoyards (produces one Gilbert & Sullivan offering a year)
http://www.durhamsavoyards.org/home.html (broken link)
There is a ballet company in Raleigh.
http://carolinaballet.com/
Plus there is a fabulous dance festival every June at Duke.
http://www.americandancefestival.org/performances/2007performances.html (broken link)
There is a repertory theatre company at the UNC campus at Chapel Hill.
http://www.playmakersrep.org/index.pl (broken link)
And of course more theater companies than I care to list that are sprinkled all over the Triangle. I don't think any are based out of Cary, though.
As for acting, most of the companies prefer to work with people they know so it can be harder to get in, but if she's interested in working off-stage (everything from costume construction to ushering) she might like the Raleigh Little Theatre.
http://www.raleighlittletheatre.org/
Don't let the name fool you; this is no hole-in-the-wall group. They have their own large, beautiful propery in Raleigh, complete with a rose garden.
In Cary she could see all sorts of performances at the Koka Booth Amphitheatre.
http://www.boothamphitheatre.com/
Check out their calendar of events. They have TONS to offer in the warmer months!
I guess I'm just trying to say that one can find the performing arts all over the place here, so I think she could be happy here.