From day 1 girlfriend!
You are the master of the herd she is in, if you say jump she should ask "How high"
If she has eating RC33 once, then that's what she shall have until you decide otherwise.
Some yorkies are picky and we have to be firm when it comes to food.
Get used to the fact that some days your yorkie doesn't eat any of the food in her bowl and some days she does. It is not only ok, but good for her stomach, as it is for ours, to take a day with no food at all.
She will not be underweight or die of hunger - I promise you.
My oldest yorkie just switched from puppy food to grownup food and she didn't touch RC even though she loved the puppy version. So I tried Hill's Natures Best and she ate that
So Hill's it is.
Now she looks at me EVERY day as if to say: "But mommy I much rather want the puppy version! Pleeeeeeeeeeeeeease...."
But she eats it. Not every day, but every other. And I put a teaspoon of oil in it twice a week for her fur and digestion.
And now - funnily, the youngest wants to eat Kalis food - which of course she can't since it's not good for her.
Good luck with it