Why are you switching her food item? Are you placing human desires on an animal that may end up ONLY taking this new food? Given how most gerbils cost more money than rats and mice, and are hard to come by... sounds like foolish idea to me.
I really think it doesn't matter as long as the BP takes it...i changed my BP to rats and now when i offer mice it wont get them...which i really don't mind 'cause i can afford to buy her some...and plus more fat = more nutrients...