She reads as dated now, and her ideas can be kind of whacky, but IIRC she was one of the first psychoanalysts to consider adult trauma as a result of parental abuse in childhood. Her idea was that Freud put too much responsibility on the abused child, and essentially left parents off the hook. I think she might have also been one of the first writers to use dead artists as examples of her theories (Freud of course wrote on da Vinci, but she fills her books with examples like Plath, Kafka, Picasso, Joyce, and on and on; Kay Redfield Jamison and others picked this up). She's basically part of the history of reactions to Freud -- people trained in the psychoanalytic discipline who then criticized or broke from it, like Laing, Horney, Klein, Szasz, et al. She's basically the godmother of the "inner child" movement, altho obviously she didn't come up with that term.
Her later books are pretty batshit, but there was a lot of stuff in this one about children who feel compelled to perform for or take care of their parents that was interesting (I remember Sylvia Plath as a big example). That said, she has the anti-mother bias a lot of early psychoanalysts do (again, the Sylvia Plath example).