She might be a slower eater, but I have heard of imprinting before.
My cinny strikes wildly at any rat that isn't white and will not eat it. >_<
I was talking with the owner of my local reptile store about it and he said he actually has/had (don't remember which) a customer who had a snake that would only eat male rats.
On that days she didn't eat were the rats white? If they were, then she's most likely just a slow eater.