Sorry to hear about you porrkitten, personally I think the first thing that needs adressing is is will you ever trust the dog with the kitten again? personally - I wouldn't and short of muzzling the dog I don't see an easy solution with this.

with regards to the amputation, you need to be steered by your vet on this one, BUT, my step daughter has a cat with a back leg missing (amputed as a kitten die to a RTA) I think they say that it is easier for them to adjust without a bad limb easier then the do should they have to have a front one amptated. BUT again, my panter had two cats which both lost a front leg and although I never met them he assures me they both led good lifes, one of them even continued to climb trees and fences.

Whatever you decide it has to be in the best interests long term of the little kitty, and judging by your email there is littlle doubt that you will not do that.
Good luck on the outcome.
please keep us informed,
regards
Sue