It seemed as if my hand was constantly in Polly's mouth as a pup! It will improve, but it takes time. Sounds like you are being as careful as I was; it seems never ending, but eventually she'll get it!
Polly would take lids off milk jugs (less than 1 second if I put it on the floor) and then hid the lid in her cheek!
On the plus side, she never bit on my hands. . .!!