Here is a link you should read. There are many out there that advise NOT to roll a dog over. I know a lot of people think it is recommended, but it really scares a dog. You want them to respect, not fear, you! Pinning a dog on its back is fearful for them.
About.com Dogs - Dog Training - Using the Alpha Roll - Alpha Rolling Your Dog
I am fostering a pup right now who is around nine months of age. I taught her not to use her teeth on me by saying in a louder tone, "Ouch" every time...and also no. Then, whenever she would lick me, I would make a big fuss and praise her. It took a while, but she no longer uses her teeth!
I suggest you immediately stop rolling her and do your best to get her out of this fear thing before it is permanent. Focus on positive training methods!
Good luck!