First of all, that's really sweet of you to go searching all of LA for a fish sandwich for your wife!
Second, here are more options nearer to you:
Cameron's Seafood Market
1978 E Colorado Blvd
Pasadena, CA 91107
111 N Los Robles Ave
Pasadena, CA zip code
Phone: (626) 405-0064
San Marino Seafood
2150 Huntington Drive
San Marino, CA 91108
-- includes $10 fish sandwiches!
I have no restaurants to recommend, but please keep in mind that many kinds of fish (including tuna) contain mercury, and women who are pregnant should be very careful about how much and what types of fish they consume. Too much mercury can cause serious harm to the fetus.
This webpage has some guidelines--
If you ever take a Sat. or Sun, scenic drive up PCH, just past Pepperdine U. is Malibu Seafood.
Tuna burger is my favorite (with extra tartar sauce).
They also have fish-n-chips (but fish-n-chips are generally too greasy for my taste).
Or, for a little more money, pick your VERY FRESH fish (halibut, mahi mahi, yellowtail, salmon, sordfish, etc.) and they will make into a sandwich.
All sandwiches come with large wedge-cut fries... perfect with the (ask for extra) tartar sauce.
Seating is outside with heating lamps.
Open view of Malibu beach = nice view.
Ample non-alc. drink options available. You may BYO wine (for yourself - dont forget to bring cork screw and glasses).
Funny, you should ask, but I just had a great albacore tuna sandwich at Julienne in San Marino (www.juliennetogo.com).
For the more pedestrian, you can also try the "Sea Wolfe" at Wolfe Burgers in Pasadena (46 N. Lake Ave.,(626) 792-7292).
Of course, there's always my old favorite standby ... the Filet-o-Fish at McDonald's.