I've had it happen twice, but with the same girl. The two years I didn't breed her, she laid slugs. She was just always primed and ready to breed, even if I wasn't. So I don't have an answer as far as if she'll do it again.
Her book also has tons of other great info as well. Even if you're not breeding for a while, I still think its a must have for anyone who owns a cornsnake. Whether you own 1 or 235, its awesome. I've been keeping corns for 16 years now, and I still reference it several times a year.When i get the corns bigger so i can get larger clutches ill more than likely buy her book to read up on the hibernation cycles.