Since you tried live and it isn't working I would stay with f/t. It's winter though, even snakes that are normally eating without problems can start fasting as they would brumate in nature. I guess that's why she won't take even live now. If she's healthy I would try to give her 2-3 weeks without feeding, and then would try boiling the f/t mice + braining/scenting. All my troube eaters love that combination.
Rat snakes are monstrous eaters most of the time, so either your girl is the exception from that rule, or she isn't really hungry. If the first one is true then you can try tease feeding to "teach" her to more actively reacting to food being presented. If she's shy around food, then you can try feeding her in a separate box that will be small enough to not give her chance to avoid the food in it (but reckon that if she'll eat in there you'll be better to leave her in it for a night, as really shy ones can regurge after putting them again in their tank immediately after they ate).
Well, that's it from me, maybe someone else will have better advice