As a woman it is understood that she may not keep nafl fast without prior permission of the husband, however Mufti Saheb if the husband doesn’t fulfill his conjugal duties for extended periods that can vary from a month to 2,3 or even 6 months ,and its an on going thing.
Yes sometimes he is angry,most times tired or don’t have time.
He has allowed wife to fast mondays n thursdays but wife feels she needs to fast more often to be able to cope with her situation.
She did address this matter with him but he doesn’t allow her to fast neither does he change his ways.
Can she fast without his permission. As its quite clear her husband doesn’t have a need for her and has no concern about his wife’s needs.
What’s worse is when he does, he does his thing but doesn’t care about his wife. Which just worsens the situation. The point is can she fast without his permission.
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
Your understanding that a wife cannot keep nafal fasts without the consent of her husband is correct. You refer to the ways of the husband and him not changing. What do you mean by ways and not changing?
In any event, seeking permission from the husband to keep voluntary fasts is not only due to intimacy needs. There are other factors related to seeking the husbands permission to keep voluntary fasts, for example, health related issues, household chores etc. 
And Allah Ta’āla Knows Best
Student Darul Iftaa
Checked and Approved by,
Mufti Ebrahim Desai.
(طب عن ابن عباس – رضي الله تعالى عنهما – مرفوعا «حق الزوج على زوجته أن لا تصوم تطوعا» لعل ذلك لإزالة سمنها التابع له جمالها أو لاقتضاء القربان في النهار أو لإيراث ضعف مانع من الخدمة اللائقة بها «إلا بإذنه» ؛ لأن إطاعة الزوج واجبة والتطوع نفل والوجوب مرجح على النفل «فإن فعلت جاعت وعطشت ولا يقبل منها» ولهذا قال الفقهاء لا يجوز للمرأة أن تصوم نفلا بلا إذن الزوج وأما قضاء أو كفارة فجائز (البريقة المحمدية ج5 ص182 علمية)
حدثنا محمد بن مقاتل، أخبرنا عبد الله، أخبرنا معمر، عن همام بن منبه، عن أبي هريرة، عن النبي صلى الله عليه وسلم: «لا تصوم المرأة وبعلها شاهد إلا بإذنه (البخارى -5129 دار البشائر)