What does she like?
If you've known her for a long time and you have the time, put together a scrap book of photo's of you guys over the years, include things like menus from your favourite restaurant, etc.
Jewlery, small necklace or bracelet.
A dress/sari, I did this for a friend who really loves sari's.
Put together a hamper for her, include her favourite chocolates, favourite bath salts, favourite sort of jewelery (small inexpensive kind that she likes wearing ie bead bracelets, earrings, anklet), and one big thing she will adore eg theatre tickets, spa day etc.
Get her a box set of her favourite TV show?
Get her a massage at her nearest spa?
Dunno its difficult to make suggestions for someone one does not know.
I've done all of the above in the past, but it really does depend on time and money, maybe get together with a couple of friends and do it.