Do you think that it has had time to heal fully? I haven't treated any broken bones yet thank goodness, but I'm glad she has the bone callus. How is she doing outside of the sling? Have you tried lowering the sling where her feet are on the ground so that she could put partial weight...
I think you are doing well so far. Various things can be used for splinting such as padded popsicle sticks, finger splints, thick layers of tape, and cardboard. This area of the leg is easier to splint than the femur. Look at page 10, and pages20-21 on this link for splinting instructions...