I think she had a very "wealthy American philanthropy" perspective of royal charity work where you turn up to a red-carpet Gala or fundraiser in a ballgown and tiara at a luxurious location (museums, 5* hotel, Stately home etc) - the rich and famous donate millions to meet and eat dinner with you and donors take the tax write-off.
It is noticeable when she does events like Invictus etc with Harry that she rarely speaks a lot to the people she meets - it's a quick "hi", photo op and then on to the next person. I found it odd that a professional actress seemingly couldn't talk to people. I'll never forget her walking away from a woman in a wheelchair at a Buckingham Palace disability reception who was trying to tell her about something.
I also think she had a very Disney Princess/Hallmark Christmas movie idea of being in the royal family. So wet Wednesdays in Wigan community centres or chaotic African villages were not what she envisaged and decided to pursue her main interest - Hollywood fame.