Traditional MOB Responsibilities
You're one woman who will wear many hats throughout the wedding planning. Your real duty, regardless of the etiquette surrounding the issue, is to get involved as much as the bride wants or needs you to be. Along the same lines, if she doesn't want you involved in a certain area of the planning, your duty is to back off.
Typical Official Duties
If the bride and her mom work well together and the bride is looking for some assistance, the MOB usually:
Establishes a budget for the wedding and the ceremony if she is making a large contribution toward the final cost
Helps the engaged couple check out various reception sites and vendors
Hits the bridal shops with the bride
Assists in putting the guest list together and works with the groom and/or his family in this regard
Helps the bridesmaids plan a shower (ideally, by providing a guest list and perhaps a little financial assistance — the girls should do everything else)
Chooses a stunning dress, and lets the groom's mom know all about it so that she won't clash
Attends parties given in her daughter's honor
Lends a hand addressing and mailing invitations
Shuffles guests' names around in an attempt to work out a seating plan for the reception (and then helps fill out the seating cards)
Helps the bride get dressed for the ceremony
Participates in the receiving line after the ceremony
Helps make sure the reception runs smoothly
Many MOBs feel as though they were born to play this take-charge role; others take one look at the workload and hesitate to get involved. If you fall into the latter category, keep in mind that, ideally, you'll only have the chance to get involved in your daughter's wedding once, and you may regret passing on some of these opportunities after the vows are said and the rings have been exchanged. This is a once-in-a-lifetime chance to share this incredibly special time with your daughter.
Essential
A wedding, of course, is meant to bring people together. If you and your daughter have been leading close but separate adult lives for several years, this is a great opportunity to reconnect with each other.
Unofficial Duties
Your unofficial duties mainly involve the things you do all the time, regardless of who is engaged and who isn't. A wedding tends to take over the lives of anyone who is involved in its planning, though; with so much talk about dresses and menus, it's easy to let non-bridal and non-wedding events slip through the cracks.
Your other responsibilities, then, are to touch base with your engaged daughter every now and then and ask how she's feeling about her impending life change. Let her cry when she gets frustrated, and take time to talk about other important issues (such as how she plans on balancing her relationship with a busy career). Also, try to balance your relationships with other people with the wedding. These are not necessarily easy tasks to accomplish, but they are as important as any of your official duties.

