The former model - who had initially been seeking £125 million from the Beatles legend - claimed Paul had wanted to offer her a lot less and said he had no compassion for the couple's four-year-old daughter Beatrice.
Speaking outside London's High Court, Heather fumed: "Obviously the court do not want a litigant in person to do well, it's against everything that they ever wish, so when they write the judgment up they're never going to make it look in favour.
"But all of you that have researched know that it was always going to be a figure between £20 and £30 million, Paul was offering a lot less than that, which you'll see in the judgment, and very much last minute to put me and Beatrice sadly through this. It's incredibly sad."
She also claimed her husband of four years had wanted to make the judgement public, something Heather claims she didn't want.
She added: "What the judge has also said is that Paul is only worth £400 million. Everyone knows that he has been worth £800 million for the past 15 years.
"Paul has always wanted it public because he wants to look like generous Sir Paul."
Heather, 40, said she will launch an appeal about the publication of the settlement, as she's worried about the safety of Beatrice.
When asked whether 65-year-old Paul had been cruel, she replied: "I can't say that for the sake of my daughter, but my sister does.
"I just want to thank everybody, especially my sister Fiona, for being so supportive for me."
Charity campaigner Heather also admitted she was "glad" the divorce is over and insisted "it was an incredible result to secure mine and my daughter's future".
As part of the deal, she will receive £14 million for herself and £2.5 million to buy a house in London. Heather was also awarded assets of £7.8 million.
The settlement will also see Paul cover Beatrice's nanny and school fees and pay his daughter £35,000 a year.
A spokesman for Paul said the singer would not be commenting on the settlement.