Welcome! It sounds like Millie is a normal weight. My puppy is 12 weeks and almost 4lbs because all she does is eat! She's the tiniest little thing w/a fat tummy, she's adorable. Some Yorkies are pickers and don't eat much, others like mine love to eat. I think urs is perfectly normal but if you'd like her to eat more maybe try a different food & new treats. All my Baby does is eat, play, nap, and follow me around. I cant really tell u what to expect cause this is my first Yorkie but I'm sure others will
I'd love to see pics of her!