The best I can offer is that it appears to be a combination of the name Ann with the prefix vo- (which, as far as I know, hasn't got any meaning beyond "a V and an O set up together").
I wish I could be of service in identifying the book your name came from, but unfortunately, I can't. There are, of course, many books that were quite popular in times past that aren't remembered at all now. The same will be true for this time period in later years--perhaps people will stare blankly when the name Anne Rice is mentioned. Even though your name is so unique, if the book is out of print (and it likely is; Google's not turning up much of anything) and out of the minds of book collectors, it'd be like trying to find a needle in a haystack.
Googling the name VoAnn does, however, bring up 32 hits. If you look through them, you have a pretty good chance of finding another VoAnn.
"What are these parents thinking?...Let's name her Madison--she'll live in her own world: 16 square miles surrounded by reality." -- Susan Lampert Smith