Wow, there are so many ideas, I guess you will just have to decide how much you want to spend or if maybe you can get all of your siblings together with you to do something way over the top.
You could set up a photo session for her to have a portrait of herself made. Have an entire family portrait made.
Maybe a beautiful piece of jewelry. A necklace, bracelet or something she would never treat herself to.
My mother likes for all of us to spend time together. It is so hard to do since we are all so busy and so are our children. She has always wanted all of us to travel together, even if it is just for a few days. Plan a trip to the Texas coast, Fredricksburg, Bastrop State Park, All of you go and stay in Wimberly and go to their "drive in" Movie (it is really an out door theater). Stay in the same hotel and plan on sight seeing or just hanging out.
Have each person write her a "love letter".. Meaning each person tells her why you love her and put it all together in a book with photos of each person.
Do a spa day for her and her girlfriends. Then have them and their spouses go out for a night of partying.
Redo her bedroom the way she wants. Build her an amazing outdoor patio in her back yard, with a covered area and new patio furniture.
If she has a friend or friends that live far away, fly them down to see her or make arrangements for her to go up for a visit with them. Send her on a cruise out of Galveston for a small trip. Send her to Vegas for a fun get away. NYC to see a Broadway show.
Anything you give her from your heart, she will love.