Go ahead, make her day. After all, she did it to improve her appearance and would probably appreciate some feedback. I'm a man who works with a lot of women, and all the talk about sexual harassment has me worried. But just because you may not be making someone's workplace unbearable doesn't mean you're not making him or her uncomfortable.
Name calling and swearing are never couth.
And while a friendly pat on the back may seem harmless, not everyone wants a shoulder-rub from a coworker.