It does no service to anyone involved to come up with an excuse, legit or not. It's an admirable quality to be open and upfront and that should never be equated with rudeness either. Life is so much more peaceful when you can be honest.
From your comment it looks like you're going to go ahead with the project, but for as long as you have that in sight it's going to keep making you angry about the circumstances. Is it worth it? Especially since there's a lot of personal emotion attached to the fact that it's for her husband, who you said you just can't stand. That seems to be the root of the problem more than the presumptuous way your friend acted with coming to you with the project to begin with.