You had such high hopes when you first met his mom. After all, this was the woman who gave birth to the love of your life, and since he's so awesome, you assumed she would be too. Wrong! You can't stand her. But the two of you will be part of each other's lives for many years to come, so you've got to make peace with the situation, and maybe even with her. Look at these three situations and how you can help amend them.
She acts hostile towards you.
She has perfected giving you the cold shoulder every time you're in the same room. One possibility is that she blames you for "stealing" her son. No, it's not coming from a logical place but an emotional one. Her child is figuratively leaving the nest (in reality he hasn't lived at home since the summer he graduated from college) but there's more of a finality to him exiting his old life when he's getting married. And by saying "I do," he's intentionally creating a tighter bond with you, his wife, than his parents. That's natural and expected, since it's the basis of a strong marriage.
What to do: Have your fiancé take his mom out for dinner for a one-on-one talk. She may need reassurance that she's still, and will always be, an important part of his life, just not the most important part (that would be you.) He should also explain that he won't tolerate her being rude towards you anymore—it shouldn't come off as threatening but matter-of-fact—and that it's not only disrespectful to you but to him as well.
She's very controlling.
Whether it's where to have the reception or what time to start the ceremony, your FMIL thinks she should be consulted on every major decision (minor ones too) you two make about the wedding. Being the family decision-maker has been her job for decades, and she has no intention of giving up that power now.
What to do: While you don't have to bow down and kiss her family matriarch ring, you can make her feel important by asking her opinion. Show her your three favorite invitation samples and see what she thinks. Peonies, tulips, or roses for the bridesmaids' bouquets? Fondant or buttercream for the cake? You get the idea. What's important to understand is the dynamic has changed—you're calling the shots here since you asked her for help. But make it clear that you and the groom are making the final decision.
She thinks that you're not good enough for her son.
You've heard the whispering and it makes you feel awful. You also heard she was like this with every girlfriend he brought home before you.
What to do: This is another situation where your fiancé needs to step in and have a talk with his mom about her behavior. In the meantime, don't fuel her fire by defending yourself. Focus on people who love and appreciate you for who you are, and be yourself at family get-togethers. Hopefully, she'll come to her senses and, with time, realize how wonderful you are too.