Patti~Linda has a lot of experience with LP and her fosters. Hopefully she will be on tonight and give you a little reassurance. I do think that you are getting a better response now that you went back and talked to the second vet.
It is very painful when their knee pops and I would agree with Ann and Kelli that the panting and licking is probably a sign of pain. The other day Ringo1's little Lucy was falling over and panting like you described and she had all kinds of bad thoughts put into her head. Turned out to be LP in both back knees.
Hang in there and stay strong for Pixie. It's so upsetting when they are injured.
