This sounds like a good time to "make your own magic!"
You can order Mom an arrangement from the Disney Florist, arrange special treats from your resort's room service, order something special to be delivered from Shirley at The Perfect Gift...
Disney pixie dust doesn't happen on demand, and I agree that you'll likely be setting yourself up for disappointment if you EXPECT surprises.
If it happens, GREAT! But if not, *you* can create wonderful memories for your mom. Remember that thousands of WDW guests each day are celebrating birthdays, anniversaries, and other special occasions.
(As well as telling the resort, you'll probably increase the attention to your mom on her day if you can get her to wear a big button or something that announces that it's her birthday... you never know who might take the time to find a way to help her celebrate!)
Have a wonderful trip!