I just wanted to offer that 1) I have tried the nipple shields (for a different breastfeeding problem), and my daughter refused to even nurse with them in place. Also, when using them, the baby can sometimes get less milk, so that's something you may want to keep in mind or check into. 2) The firm "No" and inwards pull works well with many babies (it's what my mom used on my brother and I), but when I tried to use it my daughter started to cry and went on a brief nursing strike. I found that preventative measures worked better for us. I let her chew something cold before a feeding and if I felt her start to bite I would rub her face or try to distract her with a song or something. A few times I would gently remove her and let her gnaw a finger for a minute or two.
I'm sure you'll find a method that works best for you and your baby.
Hope your "Jaws" turns back into a guppy soon!
Mattea