I have lived in SF for the last three years and I would definitely second my last recommendation for the Boulevard Cafe. It would be accessible for your mother using a walker. It has a private room in the basement that is a wine cellar/library type atmosphere (I think that there is an elevator), there are beautiful views of the bay from the main dining room, and it is consistently rated one of the best restaurants in San Francisco. I would suspect your mother would love the atmosphere. The Waterfront is very good, but not as pricey (or quite as good) as the Boulevard but it is also easily accessible. If you want something more child friendly, and much less expensive, there is the Fog City Diner, which is accessible, could accommodate large groups and has fun, interesting food. Restaurants that may be closer may not be as easy for your mother to navigate. Remember that for the rest of your group, it is very easy to get around without a car here.

Thank you for your further suggestions. I'm checking into them. You guys are terrific!!!

If you want one incredible(and pricey) meal for that group, I'd agree with Boulevard.

Boulevard is great - but here are some more suggestions.

While I've eaten at these places regularly, I find they work very well for large groups.

Lulu has huge tables that can accomodate your group. The food is excellent and there are plenty of kid-friendly choices. Basics like chicken, beef, and more. Mmmmm savory!
http://www.lulu.citysearch.com/1.html

Le Charm is a French Bistro type place that is very small - but they have an excellent patio area with space heaters. The clincher on this one is the price fixe menu. Very reasonable and repeatedly very good.
http://www.lecharm.com/

Many thanks, again!