Ya, I would be concerned. My daughter is 13mths and doesn't walk yet BUT she was scooting around on her bum at 6mths, she crawls, pulls herself up, walks while holding furniture/push toys, crawls up and down the stairs etc. From what you are saying it seems that this little one should be seen by the doctor or a specialist. It's great that she has improved since she has been in your care but not rolling over, crawl from lie down position, not pulling her own weight when you carry her etc is a concern in my eyes.