YTA.

Yes this is what i was thinking, too. The kids want to argue, then make them both do the dishes, end of story. Your daughter had a point. You don't know who was right, and who was lying. Grounding her for standing up for herself wasn't the best move, though I do agree with you OP, that you should be able to ground your child without consulting with your wife first. Yes you and your wife are a united front, and blah blah, but you both are equally able to ground your child, solo. You both know what's best for the kids, so your wife should know you will make the right decision. You don't need to check with each other for every little thing.... trust that the other parent is able to make the right choice. You've been doing this together for long enough...