This woman sounds like pure evil. She's incredibly rude and always looking to put someone down. I would not give her one bit of wedding planning information. Just give her what everyone else gets, the invitation. that's it. If she calls you I wouldnt answer. She has no right to tell you what color or what style dress is appropriate for your wedding. That's not her decision. You only have one attendant her daughter? Than i'm sure when you go to look at dresses with her you would get one that looks fine on her. did you even pick them out or is she already complaining about things you havent even picked out yet? What an effing beyotch.
You guys need to stop being nice to her. If she treats you and fi this way she'll probably treat your kids this way too. Do you really want your kids to be around someone like this? I would tell her it's your wedding and you guys are making the decisions not her. It's not like shes paying for anything. And i'm sorry to say this but your fi's dad needs to stand up for her. He shouldnt let her treat his kids that way.