40th Birthday Party for Mom?

My mom is turning 40 in November and I am only 17 right now. I want to throw her a surprise birthday party because she hates, but loves surprises. I was thinking about an over-the-hill party because she is hitting menopause really early. I have a few things picked out from Spencer's, like a "Birthday *****" cup, and some other things. But because I'm young, I really need some help. What are some fun, "over-the-hill" kind of birthday things can I do for her to remember her 40th birthday?