The 32-year-old former model, who was married to Earl Spencer, 33, brother of the Princess of Wales, and bore him four children, has issued the writ in the High Court in London against The Family Law Consortium.
They are the London solicitors which advised her before the hearing in Cape Town, South Africa, last month when she won a pounds 1,815,000 settlement after her husband sued for divorce.
Lady Spencer, who admits she has suffered from eating disorders and addiction, said she had hired the solicitors to "contain the distress" of the divorce proceedings which she wanted to be over "as quickly and privately as possible".
But she claims that because of their negligence, "one of the most public divorce hearings ever recorded took place, with the world's press in general and the British press in particular covering every detail of the proceedings".
She says that if the proceedings had taken place in England, they would have been held in private and the press would have been denied access.
"Publicity, if any, would have been minimal," the writ says.
David Hodson, senior partner in the firm, was aware of her health problems and "the damage that public and stressful divorce proceedings would have been likely to have" on her health, the writ alleges.
Lady Spencer is claiming that she missed out on a much higher divorce settlement by reaching the agreement in South Africa rather than London.
She claims that the High Court would have awarded her a lump sum in the region of pounds 3.35m. A South African court gave her a capital sum of pounds 2,065,000.Reuse content