You are confused. It wasnt by her own power that she was preserved from original sin. (You know what we mean by original sin, right?). Are you saying God doesnt have the power to preserve anyone from original sin? She receives honor higher than the other saints, but lower than the Trinity, as well she should.So why doesn't God preserve all of us from original sin then? Think of how much grief and pain and suffering could be avoided in the world by such a course of action.