Depends on your budget but what about a piece of jewellery? Normally I would say lovely glass of some kind - vase, bowl or whatever - but if your friend is moving that might be more of a hassle for her.

For my 40th a friend gave me a beautiful Wedgewood tea cup and saucer. Ridiculously expensive, but its beautiful to drink out of and it reminds me of all the fun we'e had at high teas together.