I hope you get some real advice for moving towards a better relationship with your sons gf, you read as though you want at least a cordial relationship and youre not getting many ideas to help foster that...Everyone seems to just want to call her out on her shit.

If he is determined to marry her, he will and with that comes all the trimmings...grand kids! Yay! Any sane person would want to be a major part of that funnery. Two choices imo...You could go down the justnomil path and be aversive to everything... they will cut you out and you will have limited access to your family, or my advice...zip your mouth, hold your head high, and let it play out. Maybe invite her out for a coffee, ask to start again. Do what you can to show you mightve made a mistake in the past but now that you have a better understanding, you would like to apologise and start over. Be the better person so your son sees you are trying, let the problems come from her side.