"Melania has been overheard referring to Ivanka as 'The Princess'.... Ivanka, when younger, called Melania 'The Portrait' because she spoke as often as one."

Writes Dwight Garner in "A New Book Brings Melania Trump Into (Slightly) Better Focus" (NYT). Also:

[Melania] spends much of her time with Barron and her parents. Barron speaks Slovenian...  “Trump has complained to others,” [author Mary] Jordan writes, “that he has no idea what they are saying.”...

[O]ne of her former New York roommates... told the author that Melania, in those pre-Trump days, liked to watch “Friends,” ate seven fruits and vegetables a day, didn’t drink alcohol and walked with weights on her ankles to keep toned.

Jordan confirms that the first lady and her husband sleep in separate bedrooms. He likes darkly colored walls and rugs; she prefers light ones. They rarely seem to interact. He uses Irish Spring soap....

When someone once hazarded a joke about Trump’s penis size, the author writes, Melania replied, “Don’t say this — he’s a real man.”

Donald Trump appears to dwell in the White House, for the most part, like a sultan among his pillows. Melania is self-exiled with her parents and son. On many days, Jordan writes, her press office doesn’t answer questions about where she is....

"While Melania stayed in New York, Ivanka continued to establish herself in the West Wing, notorious for its cramped and limited working spaces."

"According to several people, she was eyeing real estate in the East Wing as well, the domain of the first lady. Among other proposals, Ivanka suggested renaming the 'First Lady’s Office' the 'First Family Office.' Melania did not allow that to happen. It was tradition, and she was not going to let her stepdaughter change it. Ivanka’s office remained in the West Wing. Melania’s delay in moving from New York initially put her at a disadvantage. Even some of the staff positions and budgets that would have been available to support the first lady’s office were gone, diverted to support those in the West Wing, including Ivanka.... With Melania away, Ivanka used the private theater, with its plush red seats, and enjoyed other White House perks. Some said she treated the private residence as if it were her own home. Melania did not like it. When she and Barron finally moved in, she put an end to the 'revolving door' by enforcing firm boundaries.... People working in the West Wing say they have heard Trump criticize Don Jr. and Eric and even Ivanka for doing or saying something that the president thought was not helpful, but none could recall hearing him say anything negative about Melania.... More than a dozen past or current White House officials interviewed attributed Melania’s influence to the fact that Trump believed that just about everyone else had an agenda, except Melania. He believed she had no ulterior motive and just wanted him to succeed...."

From "How Melania Trump blocked Ivanka Trump from encroaching on her domain" by Mary Jordan (adapted from the book, "The Art of Her Deal: The Untold Story of Melania Trump")(WaPo).