I wouldn't "tease" her with a live rat like that, because it could be scaring her off the prey. I know that mine won't eat if they get spooked, which happens if the mouse/rat bumps them - especially on the nose. Just drop in the rat (don't even use tongs), close the lid, and let the snake find it on her own.

Also follow the suggestions others gave you about the tank, as that could be causing her stress as well. Finally, have you tried feeding mice and/or thawed instead? My first BP Delilah wouldn't eat for nearly a month, until we discovered she just hates rats... once we started offering live mice, she became an eating machine. Good luck!