I doubt you'd have to delve too far into your past to remember a time that you were the odd woman out. Maybe your friend got promoted instead of you. Or perhaps everyone else got asked to the homecoming dance, while you stayed home eating bonbons with your mom.
When your maid of honor is causing you disappointment or frustration, take a minute to step into her shoes. There are a million valid reasons for her less-than-stellar performance. Maybe she's dying to walk down the aisle herself, but her boyfriend isn't on the same track. Or maybe she's already married, but her relationship is swiftly heading south.
Whatever the reason, try to remember that just because your dreams are becoming reality, hers might be way out of her reach for the moment. Try talking gently and honestly about her feelings. And always remember that, even when you're planning a wedding, friendship is a two-way street. She needs your support as much as you need hers -- maybe more.