When it comes to your wedding, your mother is undoubtedly going to be extremely excited and play a huge role. While the amount of her involvement ultimately comes down to what you want, here's an outline for some customary mother-of-the-bride duties.
The mother-of-the-bride traditionally serves as the official hostess of the wedding. She greets guests at the head of the receiving line, ensures everyone has a good time, and stays until the end to send off guests. She's also seated in the first pew on the bride's side during the ceremony. She'll most likely also be the point-person between the bride and her father and the groom's parents on everything related to wedding planning. She's also the first to pick out her dress, then informs the groom's mother what she's wearing so they can complement one another. On the big day, she'll join the newlyweds on the dance floor during the first dance and make sure her daughter remains calm throughout the entire day.
As for her wedding planning responsibilities, it's ultimately up to you and your relationship, but she can be involved in as much or as little as you want. If you live out of town, she could scout locations for your and vendors. She'll most likely help you shop for your wedding dress. We're also sure she'd happily jump in as another contact when dealing with wedding vendors — handling some of the stressful logistical calls and dealing with them for her daughter. Another big responsibility the mother-of-the-bride holds is helping to compile the guest list, and run any last-minute errands her daughter needs.