Causes of pain in an older GSP

[airmedic1]

My Abby is a seven year old GSP that has always been healthy and a strong hunter. Three weeks ago we were hunting a pivot corner of switch grass when she "cried" like she had been over corrected with a collar. I know that I didn't give her any stimulation and it happened three more times in that field. I called her over and took the TT collar off. She did it twice more with only the DC-40 on her. I switched transmitters and receivers and it happened on Friday. I shut the TT collar off and she did it a few more times.
I didn't hunt her yesterday and changed receivers again this morning but when I let her out of the dog box she ran a few yards and yelped like I had over corrected her. I finally took both the TT collar and the Dc-40 off her. She would hunt a little and once I saw her standing in short grass, not moving and just cry out like I had shocked the heck out of her.
She's healthy, doesn't appear to have any sores on her chest, the pain doesn't seem reproducible by pushing on her anywhere.
Does anyone gave any idea what could be causing this?? She's a wreck, doesn't want to get away from my side because she thinks I'm punishing her. She's a good dog, a good hunter and a friend so I would like to figure this out. I will be calling the vet in the morning. Could this be something with her spine that is giving a her a sharp pain?
Any suggestions would be appreciated since my closest vet is a large animal vet.

Thanks
AM

[Sharon]

"She's a wreck, doesn't want to get away from my side because she thinks I'm punishing her."

Based on what you've said, she's in pain. Many possibilities for this... pulled ligament , torn tendon ??????? Always like to hear what the vet has to say.

[Cajun Casey]

One possibility is a luxated patella.