May want to post this on the box turtle forum...
If she is a hatchling or yearling, this is pretty common behavior. Most don't show interest in plant matter until subadulthood and even then some are picky.
If your turtle has been in captivity for some time and was raised to only eat certain foods, this is tricky.
You have to trick her essentially... chop everything fine include her favorite items along with strawberry, tomatoe, greens what-have-you. This way she gets some with each bite. Eventually, your pet reacts to the feeding instinct and you lessen the amount of meat in feedings. Then you can feed live foods and meats occassionally.
But, they definitely react much stronger to live foods than plant matter.
Paul