Congrats on your new girl! What's her name?
You have a reasonable plan: fasting for a day, then trying a bland diet of chicken and rice or oatmeal (mine prefer oatmeal to rice, and it firms up the poop well) before gradually introducing her regular food again. Pumpkin can help or hurt, so I'd leave that out for now. Olewo carrots (available on Amazon) are often helpful, and unlike pumpkin, won't potentially worsen the problem.
Not sure where you're located, but has your girl been tested for hookworms? They're incredibly common in US racers and often cause diarrhea. That's a whole other topic, but it would help us advise you better. She might also just be stressed from all the recent change.