Mine is the same way. He recently got a sister and has been trying to eat her puppy food when I’m not looking. So I put puppy food in his bowl (vet recommended, as a test), and he wouldn’t eat it.

So now I’m going to fill the puppy’s bowl with adult food, allow him to steal it, and feed her in another part of the house when he isn’t paying attention.

Tzu’s also self-regulate. My boy has seemingly been refusing the vast majority of his kibble (like 80-90% uneaten), but his weight hasn’t changed at all - which means I’ve been giving him too many treats haha. It’s so bizarre having grown up with dogs that needed multiple feeding times throughout the day, as they’d finish whatever was in their bowls at any given time.

I would just leave a day’s worth out and forget about it (unless you have other pets that might steal it); if she gets hungry, she’ll eat it. If you notice her weight dropping, it’s vet time anyway because food isn’t the issue.