My daughter is 15 weeks old and has discovered how to roll over onto her tummy. However, once she is on her tummy, she puts her head down to one side and lays there and begins to fuss and cry in frustration. Is she trying to roll back onto her back? I thought she was trying to crawl but she doesn't seem to be using her arms or legs. Is there a correct way to teach her how to roll from tummy to back?
Now that parents are putting their infants to sleep on their backs (which has reduced SIDS by a significant amount) many children are in the situation that you describe for your daughter.
What often drives development is frustration. Being put stomach down means she can't see much of what is going on around her, which is frustrating. This is good, as it will motivate her to begin to lift her head up, then, as she develops more strength in her shoulders and arms, push off with her arms to get her head up higher. Eventually, she will push off high enough to tip over and roll the other way.
To help her along, give her playtime on her abdomen, and even let her fuss a little at first. She will figure out the rest. (But still put her to sleep on her back).