But guess what - she's right. Sex is about love and procreation!
Under "Offenses against chastity," the church's Catechism says this:
By masturbation is to be understood the deliberate stimulation of the genital organs in order to derive sexual pleasure. "Both the Magisterium of the Church, in the course of a constant tradition, and the moral sense of the faithful have been in no doubt and have firmly maintained that masturbation is an intrinsically and gravely disordered action." "The deliberate use of the sexual faculty, for whatever reason, outside of marriage is essentially contrary to its purpose." For here sexual pleasure is sought outside of "the sexual relationship which is demanded by the moral order and in which the total meaning of mutual self-giving and human procreation in the context of true love is achieved."The church's Declaration on Certain Questions Concerning Sexual Ethics adds that
masturbation is an intrinsically and seriously disordered act. The main reason is that, whatever the motive for acting this way, the deliberate use of the sexual faculty outside normal conjugal relations essentially contradicts the finality of the faculty. For it lacks the sexual relationship called for by the moral order, namely the relationship which realizes "the full sense of mutual self-giving and human procreation in the context of true love." All deliberate exercise of sexuality must be reserved to this regular relationship.