I've found if we stop right then when she pulls, she will relax, stop and look at us and we can start again. If she is going really well I can praise her for it "hey that was great! Good girl!" and if she keeps pulling and I keep stopping. I tell her before we start again "Fuß" (Heel).
I was trying the lure with a treat thing, but she really is funny about not wanting to eat it. She's all "yeah, that's food. So?
" I've heard Cavvies can be particular about that.