I have a niece who is a lesbian. She told her mother that her other grandfather sexually abused her.(not rape but just as abusive sexually) She says since he did that to her she turned away from normal procreation and sex and decided to turn her affection to women.

Then her sister was abused by the same grandfather in the same manner. The sister is quite normal and has had a marriage of 27 years to a good man. A friend in Boston was a lesbian and said she was sexually abused and this made her want men and women. Her grilfriend (lesbian) says her harmones make her have men's desires.

Why wouldn't either girl accept medical treatment for sexual abuse and harmones?

It is a choice. They didn't want to stop it because they got a lot of satisfaction from it. That would be the most honest answer.