Someone else's mail comes to my house and now I'm accused of theft!?

I never ever met the person who used to live in my apartment before me. For almost a year now all her mail has continued to come to my address. I get her car insurance bills, credit card bills, bills and notices from her college, magazines, letters you name it it comes to my mailbox. At first, I just wrote "return to sender addressed moved" on everything. When that didn't stop things from coming in I began calling Capital One and Geico and the college to let them know their customer had moved and I didn't know the forwarding address and I wanted her private information to stop coming to my house. It worked like 65%. The volume of mail decreased, but still continued. Then out of nowhere I got a certified letter from her accusing me of taking "special occasion cards with gifts of cash and/or retail gift cards" and "packages with valuable merchandise and gifts". She was demanding that I return her "items" and pay her $750 in lost monies or she was going to take legal action. I called the phone number on the letter and explained to her that I NEVER opened any of her mail and ALWAYS sent it back to the post office unless it was junk flyers or magazines which I simply recycled. She called me a liar and said she was getting a lawyer. Should I be worried!? I don't understand why its MY fault that after almost a year she never bothered to do a change of address at the post office. and her freaking mail is STILL coming in! Serisouly, could I be in trouble here for something I didn't even do? I am extremely worried and upset by this.