If she doesn't want to eat, it's not good to force it because she may just throw it back up. Different if they're being picky, but that doesn't sound like the case..
As long as she isn't straining to go and can't, you have no worries about the stool right now. If you're really worried about constipation though, the vet can get an xray.
Evo is very high in fat, especially the canned. Way too high in fat for Yorkies which could be causing or contributing to the problem. I'd go with a bland diet for a couple days and then slowly transition to the old food. Problem is, if she is sensitive to chicken, this may not work. You could do whitefish or you could get a sensitive stomach food from the vet to give for a short period.
When in doubt, see the vet. You know your girl best. This doesn't sound normal for her. If there are any signs of dehydration or hypoglycemia, she has to go in immediately. A dog not eating for a day is usually not a big problem at all (even in most adult Yorkies). When something lasts more than 24 hours, I'm concerned. Anything less than that and it depends on how they look and their history. I think you would feel better taking her in, so that's what you should do.
