J.O.
I've never held to the whole tummy time thing. Babies can get tummy time many ways that doesn't require parents placing them on the floor and watching them get flustered. You can lay her in you lap tummy down, carry her in a football hold, tummy down, you can lay her on your chest and interact with her. There are many other things that can constitute "tummy time".
As for rolling over, this is another area that varies widely. Some babies can roll from 2 months of age, and others won't do it till they are 8-9 months of age. Same for back to stomach, that's the hardest and takes the longest to master. My 7th didn't master it till over a year old, he crawled and walked but couldn't figure out how to get off his back. We called him turtle boy, cause it was like watching a turtle. Funnier then heck.
Motor skills, reaching and missing is perfectly normal at this age. Just keep giving her chances to reach out for things. It's a skill, just like everything else and requires lots of practice.
Don't push it though, she'll do what needs to be done when she is ready.