I agree completely, just because crap floats your way does not mean you have to pick it up.
As I mentioned before, MIL is acting like a child by asking both of you the same questions. And there is no practical way to prevent MIL influence on W. She could just as well go straight to W with all her ideas, or your W could get her ideas from a helpful neighbor or any other relative and you would still have to compare priorities and preferences with your W. About all you can do is tell W that you already considered that option and state your preference calmly and clearly. To keep things balanced, consider also presenting the good ideas (and a few of the not so bad ideas) from MIL to your W and tell W that MIL suggested them along with your evaluation, this could possibly prevent any misconception that you are totally aginst any idea that MIL suggests.
There is little to gain by confronting MIL. Eventually MIL will figure out on her own that it doesn't really matter which one she talks to, the results will be the same. She will probably always prefer to talk to her own daughter, but with time, she will recognize that you two work together and that preference will fade somewhat.
Maybe you can think of this as an opportunity to improve communication skills with your W. Give your W the reason that planning these changes requires careful planning and cooperation. Who knows, it may be a usefull skill to have sometime in the future.
Remember to have fun with your family on vacation. Do something silly or unusual for everyone to remember.
