Masturbation, if you are a woman, often has to do with the physical need of release.

You may find yourself in a relationship that you feel is not satisfying you sexually.

Your love for this person is keeping you there, but you may need to feel a physical release after having sex with your partner, because the sexual act between the two of you did not fulfill your needs.

If you are a single woman then you may have the need to masturbate because you have no partner, and you wish to feel a sexual release. Maybe your life is too busy and a relationship would just complicate things.

via What Makes A Woman Want To Masturbate?.