Sexuality is a part of human nature, so a fully developed character is one who has feelings, and characteristics having to do with passion, sexuality, and sensuality. Not every person deals with these things in the same way. It would be ridiculous expect overtly sexual females to never exist in fiction. They certainly exist in real life.
However, skewing sexuality to simply encompass one type of sexuality or refusing to acknowledge the way those sexual feelings make a character feel IS sexist. Female or male.
Refusing to acknowledge the sexiness in the every day woman or portraying those women who are not overtly sexual as unattractive IS sexist.
Creating a character who has no feelings about life, the world around her or love, except for sex, IS sexist.
That answer your question?