(written from a Production point of view)
Christy was mentioned in Bjo Trimble's book On the Good Ship Enterprise, p. 257-259.  In it, Bjo describes the following: "Nobody knows why JoAnn Christy came to the cattle call. She is so painfully shy it is difficult to draw her out, but being an avid Star Trek fan, she found the courage somewhere. Of all the fans desperate to be chose, JoAnn caught the casting director's eye, and he decided she had the right "look" to be cast as one of the crew's few Vulcans. JoAnn returned to her seat in a pale-faced daze, so we thought she'd been turned down. "I'm a Vulcan," she said faintly. "I'm a Vulcan!"
Bjo continued, "Later she was to phone friends, in a panic, trying to withdraw from the film. She was sure she'd mess up the scene, certain she'd get ill, all was doomed! Soothing noises did no allay her fears. The dire threats of what other fans would do when they heard JoAnn had been offered a coveted place on that rec deck and backed out did it! She showed up with the rest of us."
In describing the day of the shoot, the set was is utter chaos. "The makeup artists, pushed for time, just made do with a surface effort. Some of the fans were also being put into alien makeup and needed more attention. I found JoAnn, nearly in tears, with half-cocked Vulcan ears and little else. Taking JoAnn in tow, I located makeup artist Ve Neill [...] Ve saw the problem in an instant and seated JoAnn in the makeup chair, deftly adding a bit here and there to produce a real Vulcan almost before I'd complete my request for help. Voila! A happy Vulcan!"
The 2009 DVD box release Star Trek: Original Motion Picture Collection featured a reunion of fan extras in the "Special Star Trek Reunion", including Jo Ann Nolan, David Gerrold, Bjo Trimble, Christopher Doohan, and Fred Bronson chatting on the same soundstage used for the rec deck scene.