How can I get it to turn and not ruin my copper piping around it ?

Don't understand. Bonnet nut is nut around a valve stem of faucet. How does that relate to copper pipe?

Hi Barb

I think I know what you are talking about...

Are you talking about the big chrome or brass ring like in the image below? If so, using a tool on this nut can be a problem. Instead, wrap some duct tape around the ring only, and then use your hands to try to spin the nut off (water is shut off and pressure released (open valve), of course. A strap wrench could also be useful here (google this).

If this is not the nut you are talking about then see if you can snap a picture of the valve and post it here to this thread, OK?

Mark