My 2, 3 and 10 yr old girls will sleep and lay around ALL day...if I'm just hanging out....but like others have said...if her behavior is not the NORM...then you should get her checked out...
And feeding premium food is very important to a happy healthy yorkie!!
I've seen an amazing change in my 10 yr. old rescue since we've gotten her and been feeding her EVO...from when she first came to live with us!! She's much more active and she RUNS...we didn't know she could RUN the first few weeks we had her! Now we have a hard time catching her!