[mimimomo]

I was concerned about my baby boy shaking only his left leg sometimes, so I asked my vet when he got neutered. She said he'll do what you're describing if it was patella. Don't take my word for it though, here's a link about luxated patella, & take her to the vet as soon as you can: How to Treat a Luxated Patella in a Dog | eHow.com
It sounds like your gut instints are talking to you...hopefully your baby girl will be alright.

Mimi & Momo

Proud members of Yorkies Against Puppy Mills Club