If you have some time and if it's a milestone birthday for her, you might consider making a birthday book for her. For my friend's 40th birthday, I was able to get addresses and phone numbers of her family and friends. I asked them to write a little something about my friend for her birthday and mail it to me. Then I compiled all the birthday wishes, including my own, in a scrapbook, which I embellished with stickers, paper, etc. It took a little bit of time and effort, but she really loved it. Oh, and don't forget her spouse and kids!
If that is not something you'd like to do, how about taking her for a day out or an overnight trip somewhere close? My best friend and I will occasionally take a weekend, get our nails done, take in a movie, and spend the night somewhere, just to get away. It's a win-win for everyone.
You sound like a wonderful friend who knows her well. She's lucky to have such a thoughtful friend like you. Best of luck to you!
Take care,
L.