the thing about shoulder injuries is that they pop up again when you don't expect it. i have had one all summer and it even hurts when I'm just running on the treadmill at home. they tend to linger and reappear unexpectedly.
She has chronic tendinitis in the shoulder. It's an old injury to a weak tendon in her shoulder that pops up from time to time. She's used to dealing with it. For crying out loud, she beat the most in-form player on the circuit who was playing high level tennis. She's fine.
She'll compete, and compete well. However, I think her serve has been her biggest weakness since last year's USO. I don't know what it is, shoulder or form I guess. She used to adjust better to the conditions than she does now. I know she changed her form last summer, and I don't think it's helped her percentage or her injury concerns.
Personally, I think Justine runs around her backhand too often. John McEnroe alluded to this some time ago. In the final the other day some of her forehand shots were great, but the ones where she ran around the backhand wer way off. Also, according to McEnroe she exerts more energy by running around her backhand too often. As John also said, with that backhand, why do it? When Justine^s backhand is on, it is one of the greatest shots ever!