She sounds terrified. I think she just needs more socialization. Think of it from her point of view. She's in a small cage where she can feel secure. Remember, guinea pigs are prey animals. When you take her out, you put her on the floor and all of a sudden, she's in an unfamiliar place with giant people. Do you get down on her level with her?
Do you take her out and put her on your lap and feed her? Pet her and speak softly to her.
Here's what I would do. I would first keep her in her cage and get her used to your voice. Feed her her favorite foods (carrots? Spinach?)
Once she associates your hand with good things, try to gently pet her. Do this for a few weeks. Let her know your hand is not threatening and you are not threatening.
Then, see if she'll allow you to pick her up without trembling. Next step is putting her in your lap and feeding her and petting her.
I wouldn't put her in an exercise ball. She'll be even more terrified.
This is all going to take a long time, but will be worth it. Good luck!
Here's a couple of forums which you might find helpful
http://pets.groups.yahoo.com/group/Guinea_Pigs_Society/
http://pets.groups.yahoo.com/group/GabbingAboutPiggies/
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