She wants to invite more people than your intended guest list.
Particularly if the groom's family isn't helping to pay for the event, she definitely needs to stick to the guest count. But for the mother in law with lots of friends and family, this is no easy task. This mother in law wedding planning issue is a common one. Ask the groom to help talk with his family about the guest list and to offer his assistance in making the tough cuts. It's also not a bad idea to explain why you have chosen to keep your event small, especially if you are doing so deliberately in order to create a more intimate environment.
You're having a hard time getting to know her.
Sometimes the beginning of this unique relationship isn't all smooth sailing. If you are trying to get to know her, but she seems like a closed book, keep working at it. Often, mothers in law are really worried about being too overbearing or too much like their own MIL. And in an attempt to be less controlling, they come off as aloof. Ask your groom what his mom likes to do, and use that to plan a fun afternoon for the two of you. And if she is still resistant to your charm, well, that's her problem. Be as friendly as possible and hope that you are building towards something positive in the future.
She keeps mentioning wedding ideas that are nothing like what you are planning.
You are all about the modern minimalism, but she won't stop sending you vintage tablescapes covered in lace and thrift store knick knacks. Don't immediately assume that this is a slight on your style, or even her attempt to change your wedding day vision. More often than not, this type of behavior is completely well-intentioned. Don't turn this tiny grievance into a major fight. Accept her suggestions graciously, but stick to what you love.
Her divorce wasn't amicable, and her concerns about seeing her ex at the wedding is overshadowing your plans.
One way to ruin your blissful wedding planning buzz? Constantly hearing about a terrible divorce. Situations involving divorced parents aren't just stressful for their children. As much as your groom might be dreading trying to play referee between his mom and dad, they are equally less than thrilled to have to interact. If you find that her anxiety is starting to bleed over into your happy wedding planning, be kind, but firm. Ask her what you can do to make the situation as comfortable as possible. If her requests are reasonable (separate seating and separate portraits), accommodate them and then move on. If they aren't reasonable (excluding the groom's father from the wedding), you should both sit down with her and explain why that can't happen.
She makes passive-aggressive comments towards you.
It seems like it's one zinger after another with her. Everything from how you cook a steak to what eyeliner you wear, seems to be up for an insulting "tease." If you've been patient and tried subtle hints, and nothing works, then you're going to have to nip this in the bud. This mother in law wedding planning issue is about more than this one event. It's also shaping your relationship. Try approaching her in a sincere way, just the two of you. Give her an "out" by saying that you understand it's just her sense of humor, but that these comments are truly hurting your feelings. Express that you want your relationship to be positive.