Hello Jenna Ann: I'm sorry I don't know as I can really shed much light on this odd situation. From what you wrote, it sounds as though you did nothing wrong. You scheduled a "gal pals" event & invited your daughter-in-law. That makes perfect sense to me. Personally I can't imagine why your son would expect to be invited or even want to be there. I guess I could speculate as to what is going on in your son's mind, or perhaps, what might be going on between your son & your daughter-in-law. But that's all it would be... just speculation. So I'll refrain from going there.
My personal opinion is we can never know what's really going on in another person's mind. And we also seldom know what's really going on within someone else's relationship. All we can do is to deal with what we actually observe or experience. So my perspective would be that this is your son's & his wife's issue (whatever that issue is)... not yours. And next time, I would simply not invite either one of them. I guess you could perhaps ask one or both of them what happened after things have cooled down a bit. But you may or may not get an honest answer. And, in the process, you risk simply re-kindling the fire. You yourself will have to be the judge as to whether or not it's worth the risk. Perhaps other members, here on PC, will have some better insight to offer.
I see this is your first post here on PC. So... welcome to PsychCentral… from the Skeezyks!

May the time you spend here be of benefit.
PsychCentral is a great place to get information as well as support for mental health issues. The more you post, & reply to other members’ posts, the more a part of the community you will become.

Plus there are social groups you can join & chat rooms where you’ll be able to connect with other PC members in real time (once your first 5 posts have been reviewed & approved.) Lots of great stuff! So please keep posting!