Stop trying to feed her so often. That could be part of the problem. If she refuses, just let her be and try again on the next scheduled day. You don't want to set her up on a "pattern of refusal" so to speak.
As far as why the missing part may be happening, make sure the fuzzy is in the 100°F range (live rat body temp) when you warm it up. If it's much cooler than that they won't be able to dial-in their strike as accurately as they normally would and their aim will seem to be off. It also helps to make sure the head of the prey item is the warmest part.