What makes her a "black sheep"? Mary Trump is a clinical psychologist. She earned a master's degree in English Literature from Columbia University. She has a Ph.D. She appears to be an educated and accomplished professional.
She also makes this claim about her Uncle Donald: When Mary Trump was 29 years old and visiting him at his Mar-a-Lago resort, she writes that he told her "Holy $hit, Mary! You're stacked!" when she came to lunch wearing a bathing suit. There were several witnesses to this, including Trump's then-wife, Marla Maples.
I will say it again... there is not one single form of criticism you can levy at Joe Biden, which can't also be applied equally to Donald Trump. If there is one dirty old man, losing his cognitive abilities in this race - then there are two.