I read the instance you mentioned about their row on money in Simone's book too. I don't think you made up the story. But the event happened long before. It was not because of that Diana excommunicated Simone.
Talk about who introduced Diana into the Landmine Campaign. I think I have read all Lord Bill Deedes' articles about Diana. I don't remember he claimed himself to be the one introduce her in that campaign. Moreover, I don't think Lord Bill Deedes, as experienced as he was, would take the initiative to drag Diana, who was till a member of the Royal Family after divorce, into such a political field. Through out her whole Landmine campaign, Diana had been accused meddling political things by a bunch of political figures, until two days before her accident.
In her book "Diana: the chronicle" Tina Brown wrote in a way that as if it was Mike Whitlam, the Director General of British Red Cross, who recruited Diana into this campaign. I didn't know where she got this information -- Tina didn't provide any reference to this story. But Mike Whitlam himself said the otherwise. He wrote an article about Diana shortly after her death which showed it was Diana who took the initiative. Here is a quote
The Princess called me out of the blue to have a meeting to talk about landmines. She had received quite a lot of information about landmines from the Red Cross and other organizations and she wanted to know whether the situation was a read tragedy or not. Of course, I explained the issue fully and after one hour she was convinced that this was something she could help with and make a real contribution to. The Angola trip was part of the program agreed. [1]
Plus, the trip to Angola was on Jan 15, 1997. But as early as around the christmas time of 1996, Diana had already communicated with Simmons about Landmine, as showed by her christmas card to Simmons (
''The knowledge is expanding at alarming speed. Watch out world''). Clearly Simmons was among the first knowing about Diana's anti-landmine involvement. I found no reason not to believe her.
Although Simone Simmons was a friend, and she had publicly defended Diana several times. But it seems to me she is not a kind of person who would modify or hide facts in order to glorify Diana.
On one hand she would leave comments on Amazon to defend her friends. And when Penny Junor's book ``Chales: Victim or Villian'' was publish (1998), Simone Simmons immediately came out to dispute the book's claim that Diana had made life-threating calls to Camilla.
Simone Simmons, a close friend of Diana, said: "There is no way Diana would have made threats to Camilla. I'd have known. It's just not her style. She might try to kill herself but not anyone else. ''
On the other hand, in her second book, Simone Simmons claimed that Diana had an affair and sex with JFK junior in 1995 (at that time he was single). I am not surprised if this was true. Diana was not a traditional lady. That is why many people esteem her not, but this doesn't mean she didn't genuine care people's pright and suffering. Also definitely Simone Simmons was not a decent person by disclosing such secrets. It was reported that the JFK junior story had drove Prince William into tears. But to some degree, it manifests she was a frank people, who told thing as it was.
Some people believed Simone Simmons made up the story about the call Diana received in Feb 1997, which warned Diana to stay away from the landmine issue. Well if she really made up that story, she didn't need to tell the particular name of the caller, Nichola Soames, a person who is still alive to dispute her. She could easily pick a dead person's name, so that no one can dispute her claim at all. And a lot of subsequence evidences did show that Diana had concerns over her life in 1997. (Of course, that doesn't mean there is any conspiracy about her death, coincidence can happen!!)
References:
[1] Mike Whitlam, Director General The British Red Cross, "Diana, Princess of Wales the world's most effective volunteer", Forester Lifetime Magazine, autumn issue, 1997.