Does Onyxx shower? If she does, why not go in while she is showering and take the shorts? She will have a hissy fit, but if they are not appropriate then they violate the rules. If she is wearing them that much, and to do construction and other very dirty jobs, are you allowing her to sit on the furniture? Why not have her either not sit or sit on a towel if she is in such dirty clothes? It will greatly extend the life of your furniture. As it is you may want to add shampooing the furniture to her tasks.
She sure seems determined to wear only what she wants to wear. She probably doesn't want to wash the shorts because she knows they are not allowed. In most cases your husband's approach would be what I would advocate simply because it saves wrestling over the item. In this situation there is little you can do besides either wait until she decides to wash them, they fall apart, or you wrestle her down and remove them by force (NOT a good idea, in my opinion). In the meantime, maybe y'all should make her wear something OVER the nasty short shorts when she is in mixed company or out of the house. One of my friends' dads told her she could wear any kind of shorts she wanted, any length skirts she wanted. She just had to wear longer, looser items over them! He was not above "surprising" her at the movies with a bunch of us and standing over her while she put a pair of shorts on. One memorable night he caught her before a movie with "just the girls" and was their after the movie when she was stripped down to the bandaid length mini skirt and necking with a guy in the parking lot! I am sure it was no fun for him but finally everyone got tired of the scenes when her dad showed up and told her to just wear the clothes.
Shari - the chances that cultured difficult child will stop wearing these modified tops is about zero when she is with her mom. Her mom may whine but nothing else will happen and grandma, mom and cgfg all know it. ALL you can do is to refuse to let her wear them when she is with you. I would problem shred them completely anytime I saw them just to cut down on her ability to sneak them when she is with you (and because they are so inappropriate). Sooner or later the other kids WILL say enough cruel things about them that she will stop. Chances are it will take being where other girls can see her and she hears them saying the terrible things they will say. Girls are REALLY mean about other peoples appearances at her age. Sadly it is about the only thing I can see that might motivate her to change. The worst, for her, would be to hear a bunch of the girls saying stuff to guys and to hear the guys agreeing and making cracks about it. I imagine that will hurt a lot. There is no way you can prevent it though.