. She has always been very, very alert, since the day she was born! I think she is just very observant... I can almost see her thinking... I think she will crawl if and when she feels like it.
She sounds similar to my DD (7.5 months). She watches everything but takes her time when attempting new things and isn't crawling yet either. I took her to see an osteopath when she was 5 months old. She was a very unhappy girl and I was concerned that her quick delivery had caused problems for her. While she didn't hate tummy time she would always seem very frustrated if on her tummy for more than 5-10 minutes at a time. After that first visit she has been a different baby. She had never been able to roll from back to side but started that same afternoon. She is so much happier and loves her tummy time now. While she isn't quite crawling, she's getting quite good at moving around in circles.

A couple weeks ago, I noticed that DD was getting very frustrated when on her tummy. She was trying to get up on her hands and knees. As I watched her attempts I noticed she seemed to be avoiding putting too much weight on her right hip. I mentioned it at her next osteo appointment and that night, she was straight onto both her knees.

So while I agree that different babies focus on learning different skills, there could be something subtle going on with your DD that makes tummy time uncomfortable, so maybe having her checked out by a baby osteo or chiro or physio is an idea. But if she seems perfectly happy, I wouldn't worry.

Also have you read the Wonder Weeks? It's all about babies' development and has great suggestions on how to encourage babies to explore each stage using their own interests.