Why, for true, Fergie has not been invited to Prince William's wedding?

Even though she's no longer part of the Royal Family, I suppose in other cirstances Sarah Ferguson might have been invited: she had been, after all, invited to sever family functions in recent years, even some where the Queen was present as well. However, after that cash-for-access scandal (when she was filmed accepting money for 'access' to her former husband, the Duke of York), I just can't see a situation under which the Royal Family would find her presence tolerable, even for the sake of Beatrice and Eugenie.