Isolated mitral regurgitation in children is not frequently seen. As you were told, there is often something structurally wrong with the heart, especially the mitral valve, when this is seen. Another potential problem is that there is something wrong with the left ventricle and it is dilated with decreased function. However, if it is quite mild and the mitral valve (and the rest of the heart) are otherwise normal, this can certainly be observed without intervention. Without evaluating your daughter, I cannot say for sure what her prognosis is. However, these patients typically do quite well and should not have any problems. If it is mild and the rest of the heart is normal, there is not an indication to have any specific restrictions or precautions.
To keep this in perspective, we typically talk about the amount of valve leak across a spectrum: trivial, mild, moderate, and severe. Your daughter is definitely on the lower end of this. Therefore, she is likely in no imminent or long-term risk UNLESS there is another progressive process going on in the heart. She will need routine follow-up, though, to see if there is any progression or changes over time.
She does have MVP with the mitral regurgitation. Sorry, I forgot to say that. There are just no other detectable congenital heart defects except that one. Does that change your answer to me at all? Could that be the only thing causing the regurgitation? Would having the MVP also increase the long term risk to her life? Is this reguritation with the MVP more frequently seen?