Definitely call Disney Dining back & ask if they can put a note on each of your ADR's that you're celebrating your mother's b-day.
When you check into each restaurant, be sure to mention it's your mother's b-day.
If she likes people noticing her, make sure you get her a b-day button on her b-day. (I say that because my own mother would hate people noticing her, so I'd be in heaps of trouble if I called attention to her on her b-day.) Anyway, I think the buttons are available at guest services at the front of the park.
Does your mom like things like tea rooms? If so, have you thought about scheduling an Afternoon Tea in the Tea Room at the Grand Floridian - maybe you & she can do something like that while the guys go to the ESPN club?
Do you have children? If you have a daughter, maybe you can make appts for the 3 of you at the Bibbity Bobbity Boutique.
I've read reports on these boards where some people have received little things (towel animals, balloons, cards, etc.) in their resort rooms on their b-days - so at least mention your mother's b-day at the front desk when you check-in... you never know!
I really liked the 50 pressed pennies idea!
You could also get her an autograph book & ask the characters as you see them if they'll sign their names w/ a "Happy Birthday, Mom!"
Does your mom like Christmas ornaments or things like that? Be sure to purchase some sort of commemorative item to remember her b-day trip. Also, be sure to get a really good group photo made & purchase a WDW frame for the photo.
Have fun!!