Head shots are not easy to do because digital cameras are so high resolution that it captures imperfections of the skin and need retouching so be careful.
People will wonder why u cut off their heads, well it was popularised by Peter Hurley who is a head shot specialist.You can watch his videos on youtube and you will learn things. When you shoot in colour it can distract from the subject in question even if you use a big aperture to blur the background so take note.
Ask yourself if you are merely shooting a passport photo or a head shot that the person wants to impress a propective employer.Will it get a second look? If you want to learn the secrets watch Peter Hurly especially how to do the eyes and shoulders for women.
There's nothing wrong with your photo but will it make people notice her? Peter Hurly...haha.