When is it good to switch from wet to dry?

I agree now is the time. I brought home Granite at 5 wks and started intergrating dry immediately and he was totally off wet by the and of the 7th week. Never gone back. ToedToad is right about the dental situation as well.

She could be eating dry now, mix with a little wet food, it's fine to mix for the rest of her life.

Anytime now would be fine. It is a bit off your question but Yorkies are prone to getting dirty teeth that leads to bad teeth and loss. Hard food will help that as well as brushing them regularly. I use Oxyfresh in his water to help soften the tarter build up. I try to stay away from wet anything unless it is a seldom treat.

I think that it depends on each individual dog, really. I used to work at a petstore in the kennel and I used to tell all the new pet parents to wean them off the soft food as soon as possible to start building up the strong teeth. Soft food doesn't do anything but taste yummy. The hard food cleans their teeth and gums and is just better for them, so if I were you, I'd just start putting a spoonful or two into the dish of hard food and slowly cut it back until you're just adding a touch of warm water to the food (enough so it makes the food smell better to the pooch) and then eventually just have soft food as a treat for exceptional behavior (and even then, only a spoonful at a time). Good luck weaning. If your furbaby already likes hard treats, you probably won't have trouble.