I would say that the best gift you can give your mother is your time - be there! Give her your company and your attention. Be the friendly companion we all like to have around us on a special day.
If it is impossible to be there in person then call her up on Skype and stay on the line a long time and have a good chat. And if that is impossible then spend a long, long time on the phone to her. But to reiterate, give her of your time.