I had the same problem up until last week. A Normal Female had been off feed for about 4 months. So I took her out of her tub in my rack system and placed her in a 29 Gal. Tank for a few days. Still no luck on feeding.
I moved her back to her tub in the rack and the next time I offered her food BAM!!!! she took it. She has eaten 2 more times since. Everything is the same except the change of venue for 3 days. It could be a simple as she was finally hungry.