Sexuality was created to draw us into relationships. The hormones that flow through a teenager's body awaken the desire to seek intimacy. The goal of masturbation is to bring pleasure to yourself, typically outside of relationship. For this reason, some believe that masturbation is selfish and misusing the gift of sex. While that may be the case, I don't think it is always so cut and dry.
Many women learned (or were even taught) to masturbate at very young ages. This is particularly true of those who have been sexually violated and have been "sexualized" at a young age. While I wouldn't recommend masturbation, I also don't think it should add to the shame that women feel about their sexuality. Just like men have "wet dreams," many women masturbate and orgasm in their sleep. Single women are sexual. Even those who are committed to purity in mind and body have sexual hormones, dreams, and thoughts that impact their body.
There are Christian leaders working with singles who believe that masturbation may be a way to stay sexually pure until marriage. While I would be very cautious to give that advice, I recognize that for some, masturbation is a way of channeling sexual urges away from the temptations to have sex. It's possible for the motive of masturbation to be for purity and a form of exercising self-control.
The question of motive is also important for a married woman. There is a huge difference between a selfish wife who masturbates because she is angry with her husband and a wife who masturbates for the purpose of building intimacy with her husband. Consider, for example, a wife who is separated from her husband because of travel, deployment, or illness. She wants to focus on her husband and channel her sexual urges toward him.1