Social hierarchies are clusters of complexity, which, as with most things, Traveller simplifies.
If we use Cinderella as an example, once she marries the Prince, she'd have the title of Her Royal Highness, and all subjects of the Kingdom would be expected to pay her the due respect that is attached to that title.
At best, she's upper middle class, assuming her father was a rich merchant, but having laboured away as a scullery maid, and the likelihood that no one (who counts) knew she was alive, you can drop that score several notches.
Essentially, you could view her elevated social standing score as temporary, until the Prince is crowned King, she gives birth to a son and heir, and/or she networks heavily in the salons of the aristocracy.