Have you ever wanted to be something other than human? Mermaids, half human, half fish, are one of the most amazing mythical creatures. Best known for sitting on rocks, singing, combing their long, blonde, beautiful hair. Their tail's color is based on the mermaid's personality, and reflects their true feelings. Pretty cool, huh?
Every baby is different, but most will roll over at an age between 4 months and 6 months. Rolling from front to back can be done just by kicking, which babies are pretty good at by that age, but going from back to front requires a little more upper-body (neck, arm, etc) muscle development.
Flipping from back to front often takes until around 5 months because it requires more coordination and strength. At that point, some babies take up rolling as a means of rapid transport. You don't need to coach your baby to roll, though; just make sure she has a safe place to try it out if she wants to.