I can't speak from personal experience, but looking below you have probably already seen a post by Rick Millspaugh stating his past success with breeding thayeri that weren't brumated. I've read a number of times about experienced breeders having similar good results with many different species of kingsnakes that weren't cooled and rested for any length of time. A lot of this information has been floating around in the main kingsnake forum that's pretty interesting. Browse around in there for a while and you might be surprised.
Sounds like your female has reasonably good size for a first attempt, I would say give her a chance if she is nice and healthy and has a good appetite. You shouldn't have to worry about her at all and you really don't have anything to loose. Chances are you will end up with some really fine thayeri babies.
Mike