This sounds strange...I'm not sure I know what the problem is. However, I know that a lot of yorkie's have "luxating patellas" (mine included). The vet who diagnosed her with this, said it may not affect her now (she's only 2), but later on, it definitely could. He suggested getting a surgery to fix it, before it causes severe arthiritis. I think your pup is young though to be dealing with arthiritis, but I don't know. If I were you, I would just monitor her for a couple days and see if anything changes. If not, and she still seems weak, I would definitely take her in.
However, I really wouldn't try to force her to jump or do something that might hurt her even more. It might make things worse. If your baby starts to change her eating habits, or seems unusually lethargic, I would definitely take her in asap. Good luck!! It's so scary when things don't seem right with your little one....just keep your eye on her, and I always think if I have that wrenching feeling in my tummy that something's just not right, I would take her to the vet.
