Oh Pixie and Patti
! I hope you get answers very soon, the xray is a very good idea.
The panting and licking of lips is likely from pain, she may also feel nauseous from pain - and they may lick their lips from that as well.
Since she is LP4, it makes me suspect the knee is injured and itsLP related
-or- the instability of the knee caused her to compensate - and she did something funky, and injured something
above or below the knee when the knee was "popping" or gave out a little.
Lots of love coming your way! Be strong Pixie and please get well very soon!