Her husband is not fulfilling her sexual desires so she is resorting to masturbation
Question

When having intercourse my desire is not fulfilled between me and my husband, and sometimes after intercourse is over I masturbate with my hand without my husband’s knowledge. This happens frequently. What is the Islamic ruling on that?
Praise be to Allah.Firstly: 
Masturbation using the hand and otherwise is haram for both men and women, because of the evidence which you will find mentioned in the answer to question no. 329. 
Both spouses have the right to enjoy one another however they wish, so long as they avoid menstruation and the back passage. There is nothing wrong with him masturbating you by hand and vice versa. 
Secondly: 
What you have mentioned about your desire not being fulfilled may be dealt with by speaking frankly with your husband and by each side being open and honest with the other, by each of them being aware of his or her responsibility and by both of them being eager to achieve happiness, tranquillity and love. Many husbands neglect the wife’s rights with regard to intimacy and fulfilment of desire, and this usually stems from ignorance about women’s nature and their differences from men with regard to this action. Speaking frankly, trying to deal with the matter and reading some books on this topic all play a major role in setting things straight, in sha Allah. If the woman has the habit of masturbating, that may make her lose interest in her husband and she may not feel any desire for intercourse, or it may not be enough to satisfy her. This is one of the harmful effects of masturbation that has been mentioned by specialists. 
Please see also question no. 23390. 
May Allah help us all to do that which He loves and which pleases Him. 
And Allah knows best.