Me - I would get her both, honestly. The earrings as her "real" birthday gift, and then the book just because you think she might find it useful. She couldn't really get a case of the bad-birthday-gift feelings that way, no matter what frame of mind she should find herself in on the day ("accept me as I am" or "thanks for the boost!").
I really don't think you will have any problems, tho, as you do practice what you preach and your friend knows you are Primal, so no "hidden messages" are there.
Are you all going out to celebrate, hmmm?
I have a mantra that I have spouted for years... "If I eat right, I feel right. If I feel right, I exercise right. If I exercise right, I think right. If I think right, I eat right..." Phil-SC