A woman’s 40th birthday should not limit her guests to giving her gifts that make fun of her over-the-hill status. There is more to 40th birthday gift ideas for a woman than a walking stick and coffee mugs.
The Special Number
You could give 40 roses or 40 pieces of her favorite chocolates or 40 items that are symbolic of any cause she has. You could get a cake shaped like a 40. Or list 40 things she has achieved or 40 reasons why you admire her. Take this list to a designer or use your own design to make a nice print that you can frame and present to her. A modified version would be a list of 40 things she still can remain enthusiastic about. Ask her to keep the list handy and take a peek whenever she is feeling blue. This will make her think of you and feel better at the same time, long after her birthday. You could also dig into the past and make her a photo album with 40 favorite pictures of her and her family from the time she was a baby till the present.
The Birth Year
This kind of gift requires some research. You could get a newspaper front page of the day when she was born, and frame it as a present. You could give her a gift hamper filled with memorabilia from the year of her birth--important events, music and fashions. You could also get a 40-year-old wine and toast her age with it.
You could also give conventional gifts: coffee mugs, albums, plants, books, opera season tickets, gym membership, an offer to do her share of household chores for the day or week or a home-cooked meal.
Keep an element of good-natured humor in the gift. Take care to get a card or T-shirt that is decent but funny even while making fun of her age. Depending upon your relationship with her, a symbolic walking cane or anti-aging ointment can be good gifts, too.