I Had My Mail Forwarded And Have Not Been Receiving All Of My Mail. How To Fix?

I submitted a mail forward request for my mother who has been incapacitated in a hospital for at least 3 months. I have a power of attorney for her. I get her mail at best sporadically. I am concerned that someone is tampering with her mail. I live in another city and someone stole one of her checks mailed to her. How can I follow up to ensure all of her mail gets re-routed to me? For example, she has 2 bank accounts and I only get statements for one. I am concerned that someone is not tampering with her mail and getting access to her confidential private information.