I've given mine some malt that is also peanut butter flavored.
Mine are on a grain free diet and Jane still has hairballs, but I don't brush mine. Such a bad owner, I am.
Not to be negative, as long as you are rural and the mice haven't encountered rat poison, they are good for the diet. I don't let mine eat the mice that make it in the house. Don't know if they have been poisoned.
Good luck with her hairballs.
Meowmie to Mr. Spunky, Samwise, Lady Jane, Bob, and Callie.
RIP Emily (Oct 8, 2013), Rose (Sept 24, 2001), Maggie (Fall 2003)