"Has everything" is a specific problem, not a general one
A woman who has golfed for years has solved every problem golf equipment solves. She has clubs she chose, a bag she likes, a glove in her size and a ball she is loyal to. Buying any of those again is not a gift, it is a duplicate - and in the two categories where she has the strongest preferences, clubs and apparel, a duplicate in the wrong specification is worse than nothing.
So the useful question is not "what is good". It is "what does she not have, and why not". There are only really three answers, and every pick above is one of them.
- Things that are faintly silly to buy for yourself. A heavy glass with a golf ball in it. A stencil for marking balls. A leather scorecard holder. A large photographic book of the world's golf courses that lives on a coffee table. Nobody adds these to their own basket, which is exactly why they are good gifts.
- Things she has, but a worse version of. Sunglasses are the clearest case. Almost every golfer owns sunglasses and most of them are the pair that happened to be in the car, not a pair chosen for four hours in bright light.
- Things that are useful off the course too. This is the strongest category and the most under-used. A golf GPS watch is the obvious example: it does the golf job and then it does the step-counting, notification-reading, telling-the-time job for the other 164 hours of the week.
The ball-marker stencil, and why it is the top pick
It sounds like the smallest thing on the page and it is the one with the best story. Golfers mark their ball with a dot or a line so they can identify it, because playing the wrong ball costs a penalty and because every fourth person in a group is playing the same model. A stencil turns that scribble into a consistent mark - a line, a shape, initials - that is hers and nobody else's.
It is also the single most personal golf gift that requires no size, no hand and no preference. You are not choosing something she has an opinion about; you are giving her a way to put her own mark on something she already uses. How to personalize golf balls covers the alternative - a printed custom dozen - which is the other good answer here and the better one if you want it to look like more on the day.
The watch argument, in full
If you are spending real money, a golf GPS watch is the gift we would choose for this recipient over a rangefinder, and the reason is wear time. A rangefinder is excellent and it lives in a bag pocket; a watch is on her wrist. For a woman who already has every piece of golf equipment, the thing she does not have is a piece of golf equipment that is useful on a Tuesday.
Two practical notes. Garmin publishes the same wrist-fit range for its small Approach watches as for its large ones, and the bands are a standard 20mm quick-release fitting, so a strap can be swapped for something she likes without buying a different watch - which matters more on a gift than on a self-purchase. And check her wrist and her existing watch before you commit: best golf watch for women goes through the sizes and weights in detail, because this is the one thing in the category that actually varies.
If she already owns a golf watch, the honest answer is to go the other way entirely and look at luxury golf gifts, where the picks are chosen on not being fitted, sized or a taste call rather than on price.
What not to buy her, even though the internet will suggest it
Apparel. Golf clothing for women is sold on fit and cut as much as on size, and a woman who plays regularly has worked out which brands suit her. A polo in the right size from the wrong brand is still a return.
Shoes. Size and width, five miles of walking, and a waterproof upper that will not stretch. We say this on every shoe page: do not buy golf shoes unless you can read the size off a pair in her closet.
Clubs, including a "ladies" set. A woman with her own clubs has either been fitted or has decided what she likes. A boxed women's set is an excellent gift for someone starting out and a poor one for someone who has everything - those are nearly opposite recipients.
Pink anything, on the grounds that it is for a woman. This is worth saying plainly because the category is full of it. The women golfers we are writing for here chose their own gear, and the colorway of that gear tells you what they actually like. Buy the thing, not the gendered version of the thing.
A dozen premium balls she does not play. Loyalty to a ball model is real and switching is a genuine decision for a good player, not a free upgrade - are expensive golf balls worth it explains why. If you want to give balls, give her model, or give the stencil instead.
Where this page sits against the other two
This page is deliberately the intersection of two others, and it is worth knowing which you actually want. Golf gifts for women assumes she may be new to golf and spreads across budgets. Gifts for golfers who have everything assumes a long-time golfer and makes no assumption about who she is. This page assumes both at once, which narrows it to the handful of objects above - and the narrowing is the value, because at this point in a golfer's life a shorter list is more useful than a longer one.