my baby is premature her birth weight is 1.5 kg now she is 5 month old and her weight is 5.2 kg but is it ok?and she don't roll over so when we start to sit her with support?

A. weight gain is completely fine as baby should be double the birth weight at 4-6 months and three times the birth weight at completing one year babies will roll over around 3-6 months and start to start and crawl around 6-8 months encourage the baby