Remind your mom that it's your wedding day, not hers. While that may sound a bit harsh, it's a truth that needs to be spoken. If your mom is taking charge and taking over the details and activities surrounding your wedding day, you have every right to speak your mind to let her know just how you feel. Remember to be respectful because more than likely she thinks that she is doing something good and being a help. Break it down to her in a simple and kind way.
Give her specific tasks that she is to deal with. If you don't want your mom dipping her hands in everything surrounding your big day and your decisions, then plan ahead and give her specific tasks that she needs to handle. After all, that's all she wants to do...be a help to you in any way that she can. Give her the authority to make decisions pertaining to items that you feel comfortable letting go of a bit of control on, and have your mom be the decision maker in those tasks. She'll be ecstatic to be helping and you'll feel relieved to be able to focus on the hundreds of other details that you are needing to finalize.
Let her come to you and see how she can help. Instead of thinking that she may want to help, why not let her be the one to come to you instead? She may not feel as though she has the time or energy to help and that's okay. No one says that it's a must that the mom helps out during the planning of the wedding. If she feels better sitting on the sidelines, let her.
Tell your mom that you just need her to be by your side for emotional support, and nothing more. Sometimes, we all just need our mom. We don't need her to make decisions, help out or answer questions...but just "be" with us, doing absolutely nothing. If the wedding is starting to make you feel a bit stressed out, then have your mom be the rock that just sits next to you. She'll gladly fill that much-needed role in your life.
Be open with your mom when she oversteps. If she crosses the line, nudge her back over to the other side. Truth be told, your mom may not even know that she crossed a line. The more that she wants to help, keep her on her toes. If she oversteps the boundaries, communicate with her how she did. The sooner that you can let her know that she's a bit "over-the-top", the better.
Remember that your mom is just excited to be a part of your wedding day planning. While you may have been waiting since you were a little girl to get married, she's been waiting for this day as well to show you how proud of you she truly is. Work together with her, and not against her. And keep in mind that while her intentions may not always come off the best, she has your best interest at heart.