Is it permissible for a woman to masturbate when overcome by desire and her husband abstains from marital relations?

A husband must treat his wife with kindness, and this includes sexual intercourse according to her needs and his ability, unless intercourse exhausts his body or distracts him from his livelihood. A husband's neglect of his wife's right to intercourse is an injustice, and she should inform him of it. The Sunnah (definition) indicates the obligation of giving every person their due. Even if the husband has no desire, he must force himself to have intercourse out of a desire to fulfill his wife's right and to procreate. It is permissible for a husband to satisfy his wife's desire with his hand if he does not wish to have intercourse with her. Legitimate means are available, and it is not permissible for a woman to resort to what is forbidden. There must be frankness, and the wife has the right to seek separation if the husband continues to neglect her.