Diamonds. Big ones.

White serving dishes from Williams Sonoma - I think it is their new basics line.
Some new kitchen gadgets (the cheap stuff - tongs, wooden spoons kind of stuff).
I love new sheets and/or a new blanket..

Each woman is different. Look at all the different responses.
Tell the woman, you will clean and make the meals for a week. Or how about just the weekend? So she doesn't have to do anything. Don't mention the age. Good positive words and compliments. And "yes, you are right, you are always right," and mean it.

Fun activity (tour, zip line, ethnic dance class, etc)
Pampering
Japanese green tea (from Japan) and glass kettle
Art supplies
Cups
Make up fridge
Subscription box
Flowers

day spa and lunch
taking the kids out and giving me a full day off including
sleep
overnight at a hotel with a jacuzzi tub and room service
new sweater for winter
wool socks
money toward a vacation

I just pulled up my Amazon wish list...
Some nice kitchen tongs
A trivet
An apple corer
Massage gift card
Party game (cards against humanity/expansions)
Movie theater gift card
JC Penney gift card
A few books

sleep

Someone to deep clean my one-bedroom apartment
A vegetable scrubber
A new vacuum
A new tv (after 15 yrs mine is dying)
A magazine subscription
A gift certificate to get a pedicure

A clean house. Last year dh hired a maid service to deep clean. $200 and he's now set for every birthday ever. It's all I want each year!

Let me sleep in without hearing the kids fight. You can order in dinner for all of us or get a babysitter and we can go out. I'd like time to relax on the deck. Basically, time and quiet. If you feel like buying something, a massage certificate would be great. And cake. Or chocolate.

What does this person like?

A small gift box of spices from Penzeys if she likes to cook.

Reflexology session if she's on her feet a lot.

Going out to dinner is always good.

Agree with PPs, lots of alone time (preferably pampered) and also a nice piece of jewelry or perfume.

As a Mom of two small-ish children, I would love a day at the spa. I'm not stranger to massage, mani/pedi, but just getting out of the house and doing something relaxing would be great, especially after such a long summer. I have time during the day now so I get my peace & quiet, but it's just not the same because there's always something to do. It very much won't happen.

Does she have kids? Take them for a whole day, or a good chunk of the day. Don't ask if she wants this, just say you are doing it. Take them out of the house.

What's on your birthday list? Need ideas, nothing too expensive.