Hey EricYuan,
I think the Dean of Admissions at UMKC had the quit practicing dentistry for this very reason. Other then him, I have not heard of anyone else who has encountered this obstacle.
Carpel Tunnel is a reversible condition that can be controlled. I think as long as your friend would pay special attention to how she held her hands, etc., that she would not have a problem. Perhaps she should discuss her personal condition with a doctor though.
I think that even if she did worsen her condition with dentistry that it is a rich career and there are other things that she could do with her degree that wouldn't cause her so much stress. (Teaching, public health, research). She would have other options besides just going into private practice.
Jessica