"Everything happens for a reason" is correct but often misunderstood. It is generally misunderstood to mean that God has a detailed plan, an agenda for our lives. That is not the case, we have free will and are responsible for our choices and their consequences. There's a law, called the law of action and reaction, also referred to as karma. All of our feelings, thoughts and actions trigger other developments, consequences, within and without. Her miscarriage happened for a reason, we don't know that reason. It could have been the vaccine or it could have been the way she acted (unethically).