20 yrs is a long time for everyone to say just move on. Even 7 yrs is. I don't think you must do it in person if you wanted to bring it up to her. You could call or even text if you know she's going to avoid your phone call. Or better yet have your husband bring it up to his friend since he's known him longer.
Sometimes I think of friends who faded away and wish I would've given them a piece of my mind before I 'let it go'. Why? Because it feels better to get things off your chest! One of your answers said what do you hope to gain by confronting her, well it doesn't help to let it burn inside. I would think you would hope to gain closure right?? Sometimes people need that.
So I know my answer won't be the popular one, but I say go for it if you know it will help you move on and bring closure in the end. Who knows, there could just be a misunderstanding that can be cleared up.
This may be a wild guess but how do you know the other brother didn't tell them stuff about you and your hubby the same way he did to you guys?
Does he have any reason to want to alienate both of you couples from being friends? I mean if he's saying stuff about his own brother you never know.