This is not a case of right or wrong in anyone's opinion, legal or not legal. It's a question of how to work within the entry rules that this particular quilt guild has established for their show, plain and simple. There have been a few good suggestions for the OP that may solve her immediate problem and I hope she follows up on those and lets us know how it worked out.
Most shows are now requiring the designer's name if the quilt is not an original, many even ask for what inspired the quiltmaker. I think both of those tactics are quite fair. Only a few go to the extreme that Maine Quilts has gone. Those that require written permission from a designer are shooting themselves in the foot, imho, because they are truly discouraging many quilters from entering their shows, especially those just starting out on the competitive path.