December babies

Is my daughter the only one taking her time to crawl? She sits up by herself pretty good, but still wobbly. But she doesn't like tummy time she can roll over by herself good! She just can't figure out how to roll back over and she can't go anywhere so she screams until you roll her over. My friends baby is a week older then my daughter and she is crawling everywhere. I'm not trying to rush her or anything! She can stay my baby forever! Just wondering if she's a late bloomer, if that's what you'd call it. We don't have a saucer for her. We still have to put a neck pillow around her because she's more on the tiny side. We don't have room for it in our home.. So when she's at her nana's she stands good in it and plays with all the toys! But yet she scoots herself on her back far! I don't know how she does it!