The Finding Freedom authors claim that Prince Harry felt that senior Palace staff 'simply didn't like Meghan and would stop at nothing to make her life difficult'. The incident that the authors are referring to was when Meghan wanted to try on the tiara that she and Harry had chosen for their wedding.
Reportedly, Harry flew into a rage when the Queen's dresser, Angela Kelly, did not comply with Meghan’s wishes and used offensive language toward her. The tiara, as with all the Queen’s jewels, is kept at Buckingham Palace and protocol dictates an appointment must be made to access them. Meghan had her hairdresser in from Paris for a hair practice and they needed the tiara to try. Harry interpreted Kelly’s reply as a snub and make his dissatisfaction known.
When the Queen heard about Harry’s behavior, she wasn’t having it. Kelly alerted the Queen and she summoned her grandson to a private meeting where “He was put firmly in his place.” According to sources close to the Prince, his fury was not about which tiara Meghan was allowed to wear, but about access to it.
No matter which part of the story is really true or not, you don’t upset the Queen or break royal protocol even if you are a prince of England. Queen Elizabeth makes is very clear that she does adhere to the rules of her office and won’t break them—not even for her grandson.