MIL2B and FH not speaking after argument 6 weeks ago about wedding. How can we end the drama?

Well, if she doesn't come then it is her fault. The only thing I can tell you is that she will hopefully come around. Maybe if you tell her that you're sorry, but you two had already decided on what you wanted and you didn't think it was fair that she wanted to take over since she has planned plenty of weddings and this is the only one you get to plan. Maybe give her a special job too. The rest of it will just have to be come as it may.