Probably now that she's rolling in one direction she'll work on rolling from her back to tummy next. It will just happen. My advice would be don't have a schedule for her - then you'll just be delighted at each new stage!
(Nat hated tummy time and she didn't crawl until about 11 months, but then she walked at 14 months. Phoebe enjoyed it and she crawled at I think 7 months? Then walked at 13 months, so all in all not a whole lot of difference.)