Off the top of my head (no pun) and without thinking about it too much, I'd have to say that I don't think my first thought would be that she had cancer. Most women who have their heads shaved because of cancer tend to try to offset it - wear a brightly coloured scarf or a hat or a wig, I find.
So my first thought probably would be that she was making some kind of statement. Given the way society views bald females, she would almost have to be if she was making no attempt to cover her baldness.
I don't think my curiosity would then extend to the reasons for her feeling she wanted to make the statement. I'd probably figure that was her business and move on. It could very well include that she has cancer though - and simply didn't feel she needed to conceal the fact or kowtow to society's expectations or curiosity on the issue.
LabRat
