When Tanya Andersen opens the door to her modest apartment in suburban Portland, Ore., her Maltese-terrier mix, Tazz, runs over and wags his tail in a friendly hello. The 45-year-old single mother doesn't seem like much of a fighter. She spends most of her days sitting on an overstuffed sofa with a heating pad behind her back to ease chronic pain and migraines that have kept her on disability for nearly five years. Her voice is soft and halting. Yet this woman is behind a fierce assault on the music industry and its tactics for combating music piracy on the Internet.