"Hey friend, you know, it just doesn't work for us to have company on Sunday nights. However, you could come stay over on Saturday night, or I'd be glad to come and grab a drink with you at your hotel. What do you think?"
If she doesn't let it go, or asks questions, just say "Seems like our good time the last time really kept my husband up-- he couldn't sleep with the noise. So, I'm trying to do it a little better this time around. Can't complain when he's working so hard for us." Nothing more should need to be said. This isn't blaming it on him, either, it's just a explanation. She chooses to cosleep with her son, which isn't a big deal either. That said, when I coslept with my son at that age, I made sure he went to bed at a reasonable time and once he was asleep, THEN I could join the other adults. (I didn't think they should have to deal with a tired kid because of our family's habits.)
It's called being considerate!