If you're that close, you should be able to send her a message asking, "Is everything okay? I haven't heard from you since dinner." If you're such good friends, why would she hold your son's insults against you? And why wouldn't she just tell you?
I don't think that you should involve your son at this point, unless he's in his 30s. Then, you can somewhat jokingly say, "I haven't heard from Chickadee since dinner day. Did you say something crazy to her?" Otherwise, she is a grown-up (I presume) and should be able to talk to you about whatever beef she has with you. Don't pull other people into it. Contact her once more to confirm that she is not dead. Then, leave her alone and let her work through whatever is going on with her.
(I'm sorry--I don't understand the dynamic here. You and your friend had dinner with your son? Did she, also, have a son there? Is she your "BFF" or your love interest? Did your son have significant time alone with her? Why would you think that he took that opportunity to be insulting to her? How old is your son?)
ETA: Thanks for adding details...makes all the difference.
I think that you should not involve your son. I think that you should deal with your friend only, unless she tells you that yoiur son was offensive to her. At that point, you address that issue with him. Right now, your issue is with her only. I would either assume that she's twisted up about something and write her a message to let her know that I am backing off to allow her space and will see her on the other side OR go and get in her face to ask her what is going on. Probably the former; she's already let you know that she doesn't want to talk to you right now.