She says he and his siblings defrauded her, denying her rightful share of the family business. She's alleged this in her tell-all book but now she's taking him to court.  
Sounds like Donnie's gonna get a haircut.

written off as a loon by MOST intelligent people.  I'm surprised you are giving this any play.  

And if you've watched her get interviewed, she does NOT come across as a loon but as an articulate and well-educated person. Certainly much better spoken than her crude and ignorant uncle Don.

The sheer number of fraudulent allegations and the supporting  detail in her Complaint – written like a chapter right out of The Sting -“The Grifters,” The Squeezeout” -  spell major trouble for Donald, and  his soon- to- be- disbarred sister.  

       And keep in mind they have this much apparent evidence without doing discovery, or access to the criminal investigation file. Yike.

             Further, attorneys for the lenders who made loans on Trump’s inflated assets are reading this right now to decide whether to file their own lawsuits. Either he defrauded the lenders, or he defrauded the tax authorities. One of these has to be true.

            The problem, of course, is the statute of limitations. She is trying to pretend she was “shocked, shocked” to discover the fraud after reading the NYT investigation piece in 2018. But that is going to be a hard sell given she has just published a book claiming she knew Trump was a liar and fraudster for years, objected to the probate, and “settled” her claims ( and probably waived future claims) years ago. In short, regardless of what she actually knew, she was on what we call “inquiry notice” many years ago.

               So any intelligent person would give this  a lot of play. And the sheer number of lawsuits Trump has to worry about come January 20 is breathtaking.  The Donald is going DOWN.

from the beginning, the book was just the setup for a money play for her to try to grab part of an inheritance from Fred. Its a civil case about money and so it will probably be worked out rather than go to trial, but they will be lucky if they can get a trial date by the end of Trump's second term.  No need to settle early, you wait for the clock to nearly run out.