She sounds like she is doing other things rather than rolling. DD would roll tummy to back from an early age but didn't roll from back to tummy until after she had been crawling for a while. Apparently I didn't roll at all until after I crawled so I wouldn't be too concerned about the rolling if she is sitting and starting to look like crawling. Some children skip stages eg. some kids never crawl, they just get up and walk.

Her weight sounds fine. Sometimes babies will slow down in weight gain if they are growing length wise. Check her length and if she has grown longer that month then she has probably been putting energy into getting taller rather than heavier. She has put on some weight and not lost any so it doesn't sound like cause to worry. I know DD grew 3cm one month and only gained about 300gm.