The concept of a “princesszilla” was born in the marketing division of the Walt Disney Company, although you won't heard the term spoken there. Princesszillas are adult women who purchase Disney princess branded products which are specifically marketed to adults. The trend of turning traditionally child-oriented marketing in the direction of women arose in the early 21st century, when Disney executives reasoned that adult women might yearn for a bit of romance in their lives, just as young children do.
Disney is an extremely powerful brand, and one of the strongest sectors of the Disney brand is its princesses, like Ariel, Snow White, Belle, Cinderella, Jasmine, and Aurora. Girls can watch films starring the princesses, wear clothes modeled after the clothing worn in these films, and beg their parents for an assortment of Disney princess branded products, from sheets to school bags. The Disney company is probably undoubtedly pleased by the fact that most of these products sell with minimal marketing efforts, thanks to the romance associated with being a princess.
As the generation of girls who grew up watching Disney films grew up, the company expanded the princess market, reasoning that middle class women who wore Disney princess dresses on Halloween as children might conceivably purchase Disney princess themed products in their adulthood. Some representatives of the princesszilla market can be found arranging Disney-themed weddings, complete with a princess gown for the bride; this development crosses the infamous bridezilla with the Disney-obsessed.
When Disney first began heavily producing the princess line, there was some criticism, especially from the feminist community. Some women felt that the Disney princesses might not be the best role models, and that marketing pink plastic baubles to young girls was not exactly empowering. When the princesszilla trend arose, this criticism continued; some critics believe that it infantalizes adult women by encouraging them to indulge in fantasy. It's also quite profitable for Disney, of course, because a committed princesszilla might go so far as to arrange a Disney-themed wedding at Disneyland or on a Disney branded cruise or property, thereby increasing profits for the parent company.
A little fantasy is not necessarily a bad thing; the inherent idea of “having a little princess in your life,” as Disney puts it, is thought to be charming by some women. It is also certainly possible for a princesszilla to be a successful and even powerful woman despite the fact that she sleeps on Cinderella sheets.