I've only read Horney's personality-related and object relation writings, so I don't remember her making this comment.
In fact, she stood up against perceived misogyny in Freud's theories (such as arguing for men's experiencing "womb envy" as a counter to Siggie's contention that women were driven by "penis envy").
Also, her first 1st child was born in 1910, and she began doing psychoanalysis (after schooling!) in 1919 and after she left her husband in 1923 was the support for her family, so she was obviously working in some way outside the home. (Either she didn't mean to suggest what you thought, or these experiences suggested to her that the family would do better with her at home than working long hours elsewhere -- I don't know.)
From a psychological point of view, women with children are often torn when working outside the home.
The father usually finds it easier to separate his life into work and then home, thinking little of it, while the mother has a special nurturing bond with the child and thus the child still remains fresh in mind even when she is not with him.
As per Carol Gilligan and other commentaries, women relate differently than men and are more interconnected and personal as a rule. They want to be there with the kids, while the man can have more distance without apparent distress.
Also the fact that she often wants to maintain the home a certain way, while the father is less concerned about that, usually adds additional demands that are hard for her to juggle.
As far as making her "less feminine," well, I suppose if a woman is dumped into an impersonally aggressive culture, she might adapt to that in order to survive.
Just watch The Apprentice -- eventually the people with more feminine traits (male or female) are bumped out. If the world is ultimately competitive, the masculine traits win out, and any women who ultimately advance to the Final Two (or win, like Kendra did) exhibit some masculine-type behavior even if they still preserve femininity.
(Carolyn, one of Trump's advisors, is often considered cold because of the masculine traits she exhibits. I disagree, but anyway...)
but it's hard to find things. You have to try a bunch of search terms. Hopefully something will spring up for you.
It's also hard to avoid feministic psychology. Feminism is more a social movement, but it's heavily influenced by psychological dialogue since it deals with how we think and why.