Once a woman gets married, she must always cover her hair, even if she C”V gets divorced. “
That is not necessarily the halacha. I am acquainted with many women who were given the heter to take off the head covering after their divorce, so that men would realize they were available again for marriage. They were otherwise very frum women who always wore a shaitel. Some women feel uncomfrotable with the idea, so they would not do it. But it is not for us to judge either way, especially if they have a p’sak that permits it.