Sunday night dinner or Sunday bruch?
OK, I am a bit older than your mom, and love brunch. Not sure if this will help, but we like:
Brennan's for brunch
Ralph's on the Park for brunch
Though both in the Brennan "family," they are quite different, though both quite enjoyable.
When flying out, we often leave on Sunday PM, so will choose Ralph's, as it is a tad closer to MSY. If we are staying over for a few days, then Brennan's.
I would call either of those, and let them know of the special occasion. Either should be able to make it memorable, and wonderful.
Now, with the schedule, you might look into The Grill Room at the Windsor Court Hotel (depends on where you are staying) for a great, special dinner. Note: that is in no way the ONLY possible dinner location - there are many, many more, but they are elegant, refined, and have been great, over the last 10 years.
Enjoy, and Happy Birthday, to your mom.
If you want to dine in the FQ go to Antoine's or Arnaud's for Sunday Jazz Brunch. I like Antoine's the best. Be sure to check out Hermes Bar at Antoine's or French 75 Bar at Arnaud's. Mr. B's has an outstanding Sunday Jazz Brunch. It's across from Hotel Monteleone. I also like Muriel's too.
In Mid City near City Park is Ralph's which has a fine SB and outdoor dining. Redemption is a neat restaurant in an old church in Mid City. If you go to the GD or Uptown go to Coquette or Patois for Sunday Brunch. Cafe Atchafalaya has a Sunday Jazz Brunch. I really like CA. It's a unique neighborhood restaurant near the Irish Channel W of the GD.
Dante's is Uptown and has Sunday Brunch.
Antoine's @ 713 Saint Louis St., New Orleans, LA. 504 - 581 - 4422.
Arnaud's @ 813 Bienville Street, New Orleans, LA 504 - 523 - 5433.
Mr. B's Bistro @ 201 Royal St., New Orleans, LA. 504 - 523 - 2078.
Muriel's @ 801 Chartres St., New Orleans, LA. 504 - 568 - 1885.
Cafe Adelaide @ 300 Poydras St., New Orleans, LA 504 - 595 - 3305.
Ralph's on the Park @ 900 City Park Ave., New Orleans, LA. 504 - 488 - 1000.
The Columns Hotel @ 3811 Saint Charles Avenue, New Orleans, LA 504 - 899 - 9308.
Coquette @ 2800 Magazine St., New Orleans, LA. 504 - 265 - 0421. http://www.coquette-nola.com/index.html
Patois @ 6078 Laurel St., New Orleans, LA 504 - 895 - 9441. http://www.patoisnola.com/
Cafe Atchafalaya @ 901 Louisiana Ave., New Orleans, LA. 504 - 891 - 9626.
Here's a link to Sunday Brunch restaurants in NOLA.