6 month old (preemie)

Catie

So I know every baby is different, but I'm just trying to get a "general" idea of what all my baby should be doing right now. She was a preemie and they said she could develop slower than other babies her age. Right now she can roll over (really well since like 5 weeks she's been rolling over) she scoots across the floor, holds her head up well, holds her bottle, she talks a lot (babbles) she can say mama and daddy and love u, but she's not sitting up on her own or crawling. She's my first so I really don't know what all she should be doing. Babies around her age (my friends) have already been sitting up and doing other things. And everything I read online is different. So I just need some opinions! Also any suggestions on helping her learn to sit up alone? She can supported (for a few seconds then she rolls over on her tummy) I want her to grow at her own pace but if I'm not doing something I would like to know so I can help her as much as I can develop like the other babies!