She looks like a Yorkie to me...and looks like she'll be a dark princess when she gets older! (I personally love when their coats stay dark ^_^)
Jack will be 5 months on the 25th and almost weighs 6lbs already. He weight 3.2 at 10 weeks when we brought him home. He isn't chunky either, just has really long legs and only a small bit of fluff in his coat. I assume he will be a big boy when he is full grown, which I don't mind one bit. As long as he stays loveable and healthy
I wouldn't be too concerned, honestly. She looks perfect & so so pretty. If she's happy and healthy, then you're blessed!