Unless you have a close personal friendship with her, I would stick to joining in any group gift for her. If no one else at work has suggested it, then you could make the suggestion and organise a collection (assuming this is normal / permitted where you work) If you work more closely with her than others do, or want to add something, then you could also send a card.
If this is not the normal practice, then I think it is a lovely thought to send her something but I would buy rather than make, as Pastry Goddess suggested.