With little turtles like these the fibreglass bonds to the shell and doesn't shed properly, so it deforms the shell as it grows. Also it gets very hot as it cures, which is bad news for reptiles.

If Shelley had a larger, gaping crack I would use fine wire and superglue to suture the wound shut. When the wound healed I'd just cut the wire off and let the rest shed off naturally over time.