Rattle The Cages

Straight up.

DEAR JERKASS: My fiance, "Todd," and I just became engaged and are starting to plan our wedding. The problem is his father is remarried to a terrible woman. Todd grew up with her, but he can't stand her, and I feel the same way.

I gave her a chance, but she got drunk -- something she does often -- and insulted my mother. Obviously, my mother and Todd are my priorities.

Todd and I do not want her at our wedding because we're afraid she'll get drunk and make a scene, but how do we manage that? How do we make it clear that we love his dad and want him there, but his wife is not welcome? -- NERVOUS BRIDE-TO-BE IN FLORIDA

DEAR ENGAGED TO A JELLYFISH,
Todd needs to do this, not you.  He needs to go to his step-mother and tell her straight up that he doesn't want her at the wedding. If he wants to have his father there while he talks to her, so be it.  He needs to tell her that her actions are what have prevented her from going to the wedding.  That if she had behaved like an adult, and not just an aging teenager with a chip on their shoulder, then she would have been included in the wedding.
Depending on how far away the date of the wedding is maybe, just maybe, you would be interested in making a deal: if she can go to enough Alcoholic Anonymous meetings (or an equivalency) then she might be allowed to go to the wedding.  AFTER she aplogizes for what she has said.
Here's the problem, though.  Some people should be drunks because at least they pass out.  If she sobers up there is still the chance she's going to be a bitch.  If you make a deal and at the wedding she gets drunk, have a few of your more burly relatives ready to eject her.
There comes a time when you need to cut people out of your life.  The wedding is going to be the least of your problems.  His father is family, and family is going to be there long after you get married.  So it may come to cutting them out of your life entirely.  Is Todd ready to do that for you?  Are you ready to ask that of him?