LOL ... I have so been there and you really are bringing up a lot of old memories. My DD never wanted to be held like a baby always doing the stomach crunches to sit up and be held sitting up. Just remember that those stomach crunches are strengthening her abilities to sit independently. And Grinity is correct ... tummy time is important so one suggestion I can give since my kiddo never liked tummy time was to place a pillow on your lap and lay her on her tummy patting her bottom. You can do this in short increments and build up on it.

And the changing diapers issue if I remember correctly I explained to her what I was doing it and why she needed to lay down until I was done... sounds crazy I know but it seemed to eliminate the crunch issue during diaper changing time. But it just proved how locked she was in her body.