First off, you haven't said you've had her at the vet for a check up and see
what the vet thinks about this.  Four years old seems kind of young to stop
playing.  The cats love those interactive toys on a string that you can't
leave them alone with because they can get caught up in them.  Some people
play with a laser light in the wall with their cats.

--
Barb
Of course I don't look busy,
I did it right the first time.

Have you tried "Cat Dancer" and/or "Da Bird". My one cat is like this. And
she really wants to play too, but doesn't like to play in front of the other
cats. She does get zoomies when the weather is crisp and I open the deck
door for air. She is much less prone to want to play during hot weather. I
do wonder at the sudden change of attitude. Has she seen a vet?

What was she eating before you got her, and what is she eating now?

I saw the reverse happen when I switched Oscar from dry food to wet.
Suddenly, she's all kittenish again!

Also, while Oscar isn't terribly interested in most interactive toys, she does
adore the cat dancer.  It's about $3, so if she doesn't like it, you haven't
lost much money.

She is just being a cat. :) Persnickety and quixotic. The same toy
that drives my cat nuts one day is looked at with boredom
the next. Get her a variety of toys, and realize that there are
times when she just does not want to play.

New toys. Perhaps she is bored with the old ones. I'm always on the
lookout at the Dollar Store for things that might amuse them, bags of
little balls or feather dusters. Some of mine are especially
interested in the things in my night-table drawer. One fishes out
emory boards, one pencils, another Q-tips.

Then there's the big boy who likes to pull dirty clothes out of the
laundry hamper and cuddle up with them, but that's a different story.

BarB

New or challenging toys. Play with her. Each time we go to the pet store for
cat food, my husband tries to cover my eyes so I won't see the new toys but
of course that isn't about to work. Our cats may be a bit over indulged with
toys but they enjoy them. There are the usual balls and crinkle toys and
love their mice but turbo chasers, turbo chasers with balls inside the
middle and mice on the top... it all adds to their day of play.

Try different things and see what they like. Laser pointers (kept away from
eyes) are great too.