A 29-year-old woman suffering from brain cancer who became an advocate for terminally ill patients who want to end their own lives has died using Oregon's doctor-assisted suicide law, an advocacy group said Sunday.Brittany Maynard "passed peacefully in her bed surrounded by close family and loved ones," according to a statement posted on Facebook by the group Compassion & Choices, an Oregon-based nonprofit that assisted the young woman through her end of life.Maynard was diagnosed in January with a glioblastoma brain tumor and said she planned to take prescribed medication to die when her pain became unbearable.She and her husband moved from the San Francisco Bay area to Oregon this year to take advantage of the state's Death with Dignity Act which allows terminally ill residents to end their lives with the assistance of a physician.Four U.S. states beside Oregon allow assisted suicide.Messages of support poured into social media upon word of her passing."Thank you for paving the way for the future of death with dignity. You were a bright vibrant light in the world and you forever left your mark. Prayers for all family and friends," one user wrote.Opponents of assisted suicide say some people who are ill, especially among the elderly, might be unduly influenced by people close to them to end their lives and that other ways exist to ease the suffering of the terminally ill.Maynard, who has stressed that her decision to end her life was her own, had previously told People magazine that she had picked Nov. 1 as the day she planned to die.On the website of Compassion & Choices, Maynard said she had a bucket list of activities she wanted to complete, including traveling to the Grand Canyon, which she ticked off last month."It is people who pause to appreciate life and give thanks who are happiest. If we change our thoughts, we change our world! Love and peace to you all," she wrote in her own obituary.