According to Andrew Morton, Diana was trying to build public anger against Charles so that he would be forced to renounce his right to the throne, he and Camilla would leave the country, and Diana would be left to groom William for the throne.
I'm sure she convinced herself that it would be best for William, but she failed to consider whether William and Harry wanted their father to leave the country.
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If this is true, she also failed to consider that what she was doing was actually treason under the 1702 Treason Act and I would be very surprised if her advisors did not tell her that.