Please be advised that nursing school is the Hunger Games- everyone is out for themselves. You guys are only three days in and she's already proven to be a controlling friend. There might be a point where you witness something in clinical's and if she has you tied around her finger, you will not tell on her; she might blame it on you and then what? I don't trust people when they have a personality like that, they always have an alternative motive. I would find out the policy about cheating and read it. You might be just as guilty as them just for knowing about it. When I was in nursing school, there were people passing around the "professors test bank" to the books we had and most of our instructors would pull questions from there. I avoided studying with these people, and I always brought it up "if you guys have the test bank, I don't want to be involved, nor do I want to know where it's coming from."
Do not go to study groups with this girl, you guys will all be charged with cheating. If it's still bothering you, go to an instructor; you will feel guilty, but much better.