Yea, that's what America was like 35 years ago
Actually it wasn't. She started working at the bank in 1960. In 1967 was taken to Indonesia at the age of 6, so is unlikely to have been aware of the progress of his Grandmother's career. When he returned in 1971, she was already bank VP, so unless he is grousing about them not making her Bank President, he could have observed nothing of her being denied promotion.
Obama’s grandmother was born in 1922. Prior to she and her husband Stanley moving to Hawaii in 1960, she worked in Restaurants. She found a job at the bank in 1960 at age 38 and became a vice president ten years later at age 48.
Ten years for a former waitress entering the banking profession at the bottom to rise to a vice president is quite impressive. Particularly when she entered the new profession in middle age. Also given that she was a member of the white minority which was discriminated against in Hawaii at that time. Plus she was one of the first female vice presidents at this bank. None of this story suggests discrimination against grandmother Dunham because she was female. One might actually argue her rise was very quick given her background.
With only a high school education, it sounds as if she wasn't treated too badly.