There was some negative press around Camilla being lazy, and being a personal support to Charles but not being particularly involved with the charities/royal visits etc. at the time they married.
Maybe HM shared those concerns, but having seen her work hard and make a place for herself with most of the general public, she is now confident in her becoming Queen Consort.
After all, you can promote someone from Princess to Queen, but it would have been jolly difficult to demote an 'intended' Queen to Princess.