Well, turns out she's doing just great. When I asked the doctor if I should be worried that she isn't sitting independently yet, he directed me to sit her on the table. As she sat there, he asked, 'so what's she doing now?' I told him she has a tendency to fall over. He said she is strong, has good balance, and her problem was likely that she didn't know how to control moving from one position to another. Another worrywart mother...
Here are the stats: 15 lbs, 6 ozs. and 27 inches. The nurse said she's just under the 50th percentile in weight and at 90% for height. I'm still wondering why I get countless remarks about how "petite" she is. I am going to start taking it as referring to her features rather than her stature.
Overall, she is still a very happy girl. Her eating (baby food) is improving as is her sleeping. She's sleeping about 6-8 hours in one stretch. I know that's not a dream, but it's getting better. We're also still waiting for those first teeth to peek through. I sense a lot of changes on the horizon. As exciting as that is, sometimes I'd just like to bottle her up, just as she is.
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UPDATE: As of this afternoon, she's up on her knees. The belly pivoting may be on its way to crawling. Yikes!
SECOND UPDATE: By evening she had mastered the "plank" pose, basically the straight arm pushup.
THIRD UPDATE: I am now confident that she can pass an object from one hand to the other. Phew!