It is obvious to me as someone who works in the Theater industry that the authors are ignorant of how theater works and the people making comments are too. Let me Help you all here.
The Design side of the theater industry is very competitive. Many producers are unscrupulous. You need to remember that on the commercial level such as Broadway and the West End and the associated tours this is not art it is big business. Designers struggle away throughout their entire careers working for peanuts in hopes of landing a "Riverdance" or "Cats" scale show. When I say peanuts read that as below minimum wage.
Design contracts are structured in such a way so that the designs are the possession of the designer and productions commission the designs and pay a fee to the designer and to have the designs built. They are subject to approval from the producers, but all changes must be approved by the designer. The designers union has negotiated royalties with producers for use of the designs on a specific production or tour. When those contracts expire, the producers must either extend the contract or redesign. It is always cheaper (on a union contracted production) to extend the contract rather than have new sets or costumes built.
I have no doubt that the designer in question has been fighting this battle for years with these producers, and the fact that it is getting to court only now is understandable.
As for the comparison to fashion designers...Costume designers are way more talented than fashion designers, and the unique requirements of live performances, 8 or more times a week, demand that they make unique one of a kind clothes that will endure the stresses of live performance. They don't smear their names over every piece of clothing they make, can you name three costume designers?
The history of this kind of abuse goes back over 100 years. I have worked in the industry for 20 years. I hope She wins her case.
For the record I hate Riverdance and King of the Dance and am no fan of Mr. Flatley.