Im my experience when my BPs fast its only temporary.
They will usually POUND food after a fast, and stay consistant for a while.
I would try waiting a couple weeks then offer her a live rat, let it stay with the snake for maybe a half hour, checking on them periodically so the rat doesnt harm the snake.
You can even do small prey, such as a weanling rat may intice the snake to strike.
Ive had a male fast for 3 months and drop about 100g but now hes eating great and gaining again.
Good luck with your snakey!