Lolx well im happy everything worked out for you.
I took your advice mother in law told me her reasons for asking for her to be invited was to not give her any more ammunition and she never intended to upset me sis in law said he didn't want to come so everyone is happy lol xx
Just send her an invite so mother in law will be happy. Your sister in law can't say you didnt try to invite her. No guarantee that she'll show up or not if she's that angry over complete stupidity