Unfortunately, without seeing your daughter, I cannot say what, if any, restrictions are required of her. It does seem good that she has preserved function and has had no specific arrhythmias or problems. My recommendation is that, especially for something so important as physical restriction in the face of a cardiomyopathy, you obtain a second opinion by a cardiomyopathy specialist. These are folks who are pediatric cardiologists who specifically deal with these abnormal hearts and can advise you regarding the latest research.
As I write this, I realize that this is an expert forum. I still want to write this to you as a mother who has raised a child with a severe form of concentic hypertrophic cardiomyopathy. First and foremost, you MUST listen to your child's pediatric cardiologist! He knows what is best for her wellbeing. I have traveled all over the world and this country dealing with more pediatric cardiologists then I care to count; several have become very good friends and one is actually my daughter's godfather; I have yet to meet ONE cardiologist who wanted, or liked, to restrict a child/teen from sports and like activities. For the most part, they hate doing that because they realize the impact it can have on those kids. Go back and talk to your PC about this; many times there are activities that children can do that do not put as much strain on the heart. My daughter, for instance, learned to ride. An MRI and echo are not apt to show arrhythmia problems, not is a stress test UNLESS the arrhythmia shows up at the exact same time the test is being done as the EKG is the primary way to first check for arrhythmias, sometimes something can be picked up that may make a doctor consider the possibility of an arrhythmia issue popping up. Has your daughter had a 24-48-72 hour Holter done or has she had any arrhythmia problems? Sometimes children will have a King Of Hearts monitor put on for 30 days to help check for arrhythmias. Your daughter is 17 years old at this point so unless she is going to college and her sports are helping to fund that education, her sport's career is beginning to come to a close. As a mother, you have to ask yourself: is this sport life she is involved in worth her life?