In Islam, masturbating is haram. If the woman is married, it is her husband's duty to satisfy his wife's sexual needs. It is very oppressive and selfish if he does not. We have numerous hadiths that mention this as well.
If, for whatever reason, the husband is not fulfilling his duty and catering to her rights, it does not give her permission to do haram, and she must address this with her husband, or find other solutions.
And Allah knows best.