Since no particular "gift" ideas come to mind, how about you create categories for "how well do you know her?" and ask everyone at the party to tell a story about certain topics that are near and dear to her heart? Have a picture to accompany each. Is this an all-adult party or no? That might drive some of the questions.
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Gift-giving is not about the gift but the recipient of the gift.
You have been this close for so very long. You want to give her something that she will cherish, but you ask people who know nothing about her...or your relationship with her. You need to go to the heart of who your friend is and what's important to her...and choose from there.
We can surely help you find something "cool", but you want it to be more personal than that.
Good luck, B..