Yeah---don't give up. On a previous thread, I mention that we are kinda expecting similar problems with our next two to start as you are having with Tyler and Gracie.
The first two have been easy. Zeke the puppy is a pup so he hadn't been kibblized very long. Wolfie the oldster was doing the raw diet way before we started him officially. As best as we know he has caught and consumed at least 36 squirels-2 groundhogs and 1 opposum. Only differance for him is that now its being eaten indoors.
Now the other two when they start, I am going to feel your frustration. Our lab mix is only now getting the hang of chicken feet. I actually don't think he knows what to do at times as he has always been a slow learner( house breaking, sit/stay etc). But by god once he has it figured out, it is set in stone.
Our boxer is the one that truly needs to do the best diet available. Boxers are prone to cardio problems, cancers, allergies, eplisepsy,thryoid problems and more. My boxer and your bulldog are very related to each other by breeding. She has a hard time crunching the chicken feet which is probably due to the crazy offset dental pattern.
I don't have a suggestions, as also being a novice. But I lurked around this site for a number of weeks before starting up. The responses to questions read here by the experienced feeders will really be invaluable.