To describe a woman's skin as white, you can say "her skin is fair" or "her skin is pale." You can also use adjectives such as "alabaster" or "porcelain" to describe the whiteness of her skin. Be aware that using certain language to describe skin color can be loaded and potentially offensive, so it's important to be mindful of the context in which you are using these terms and to be respectful and sensitive to the person you are describing.