I dont think your in the wrong at all. From what I understand it is whomever is helping financially with the wedding you include on the invitation. I know its a tough situation especially since it is your mom and it sucks having people mad at you, (especially other family) but try not letting it get to you. This is YOUR day and you only get to do it once, so its only fair that you do what you and your FI truely want to do. It was her decision not to help financially with the wedding, and personally I would find it unfair to those who are helping to have her name on the invites. If she's not helping you out or even attending the wedding for that matter, then her name shouldn't be included on the invite. (If that makes sense lol). I'm sorry if I sound like a complete cow the way I worded that, totally not my intention was just trying to make a point. Good luck!