If your mom and your maid of honor don't get along, that's pretty unfortunate since it can affect the entire bridal party and the wedding. Why are they such archenemies anyway? Maybe they're involved in a power struggle over which of them is more important to you. (Does there really have to be one top dog?) Or maybe it's more of a personality thing (both are Type As) or they disagree over style (your MOH wants to hold the bridal shower in your favorite Mexican restaurant; your mom insists on having the bash at your rich cousin's house). Whatever the problem, it should be theirs, not yours, yet you somehow ended up in the middle. While you may not be able to arrange a truce between the warring factions, don't let their antagonism for each other stress you out. Grab a calming drink and read on for ways to handle the fight of the century: MOB vs. MOH.
Listen to their complaints
Speak to them separately to find out what the problem is, if you don't already know. Is it one major incident, several small ones that have ballooned in importance, or a misunderstanding? Knowing you're listening will show them you care.
But don't choose sides
The worst thing to do is to side with one of them and alienate the other. Think Switzerland and remain neutral.
Try to mediate
Bring them together for a chat, and tell them how their behavior toward one another is making you very unhappy. If they can't resolve their differences then and there, tell them the meeting is over. You have better things to do, like pick out an invitation font or debate fondant versus buttercream.
Keep them apart
You dreamed of going wedding dress shopping with Mom and your MOH. You always pictured the ladies chatting and laughing and voting yay or nay as you tried on one gorgeous dress after another. But—reality check here—having your mom and MOH in such close proximity wouldn't be a dream but a nightmare. So instead, take them shopping separately. Assuming you'll be visiting more than one dress shop, take Mom to one store, and your MOH and one or two bridesmaids to another. This lets each woman have the thrill of seeing you in white without them seeing red.
Don't give in to guilt
Your mom knows you aren't going to replace her in your life but she knows you can always replace your MOH. When she starts talking about how another bridesmaid should be "promoted" and the current one thrown to the curb, don't let her think she can strong-arm you. Tell her that the topic is off-limits and change the subject. When you don't give her a platform to air her grievances, she'll likely give up.