If she's eating live mice, you need to try to switch to either live rats or F/T mice first, then to F/T rats - you're making her make too big of a jump all at once. And make sure it's warm enough when you offer - there are tons of threads on the forum about switching to F/T, if you haven't used the search function yet. If she refuses, just track her weight with a scale - time (a week, a month, three months) isn't nearly as important in waiting her out as watching her weight. I just can't see giving up an animal because it doesn't eat as often as I would like it to, even though it's healthy.
One add: Unless you're intending to feed her gerbils (I don't recommend), I would stay away from gerbil bedding. However, dirty mouse bedding would be worth a shot since mice are what she obviously likes.