Is it permissible for an unmarried woman to read sexually explicit material to quell her desires, and will Allah accept her repentance despite repeated sin, and will she be completely forgiven as if she had no sin, given her fear that her religious knowledge will be stripped away because of this?

The door of repentance is open, and Allah's forgiveness is immense, no matter how many times a sin is repeated. Do not despair of repentance whenever you sin, and strive to achieve sincere repentance, for Allah accepts the repentance of His servants and forgives evil deeds. If you repent to Him, He will not deprive you of the light of knowledge, nor will you deserve punishment.