As it is wajib for men to grow beard, in the same way it is also wajib for women to grow their head hair. So, it is haram and unlawful for women to cut their hair. The adornment of women shall vanish by cutting the hair of head.
Note: However, if the tip of hair splits that prevents its growth then you can cut the hair ends so that the hair could grow longer.
Allah knows Best!
Darul Uloom Deoband