My baby doesn’t crawl

So my daughter is 8 months old. She was burn premature (35wks) and was in Nicu for 2 wks. She is really good now and healthy; matter of fact she eats a lily bit too much hehe. But i cant stop myself questioning that why she hasn’t learn how to crawl. I see kids that are already doing it, for some reason she does like the position that she wants to do it but doesn’t do it also she doesn’t sit by herself. If we sit here she stay there sitting with no support but she wont do it by herself and I’m afraid that she might have a delay idk. She seems fine and healthy and active but idk