Mother's Day in San Pedro
While I haven't been to this place (Beach City Grill) http://chowhound.chow.com/topics/892091 that "flowergirl" wrote up here on CH, it sounds like something I'd enjoy. Too funky for your mom, maybe? Take a look at the Yelp photos. The food looks really good and the inside booths look comfy and clean http://www.yelp.com/biz_photos/beach-...
My wife and I also like 22nd St. Bar & Grill as recommended above by chpskt.
San Pedro doesn't have any outstanding restaurants. However:
Twenty Second Street Landing is a solid seafood restaurant.
J. Trani's for white tablecloth Italian or seafood.
Think Prime for steaks.
The best food in Pedro is over the counter Mexican, but that's probably too informal for Mother's Day.