The family of an American woman killed while being held captive by Islamic State militants is holding a final memorial service Saturday in her hometown.

Kayla Mueller, 26, was an international aid worker who was captured in August 2013 after leaving a Doctors Without Borders hospital in Aleppo, Syria, and held for 18 months.

She was honored last month at her alma mater, Northern Arizona University in Flagstaff, and at a candlelight memorial held by churches, schools and community groups in Prescott, a mountain community of 40,000 where Mueller grew up.

Sen. John McCain is scheduled to deliver brief remarks at Saturday's memorial, while Mueller's family said they'll offer personal reflections of her life.

In Prescott, Mueller helped raise awareness of HIV and AIDS and volunteered for the overnight shift at a women's shelter.

She protested genocide in Darfur, Sudan, while in college. She also traveled to the Palestinian territories, Israel, India and France.

Mueller's parents have started a nonprofit organization called "Kayla's Hands" designed to further her humanitarian efforts locally and internationally.

Mueller and her Syrian boyfriend were taken hostage. He was released but returned to Syria to try to free her. Mueller became interested in Syria after her boyfriend told about the struggles of refugees there.

Her death was confirmed Feb. 10 by her family and U.S. officials. The militant group claimed she died in a Jordanian airstrike, but U.S. officials have not confirmed that.

Mueller is the fourth American to die while being held by Islamic State militants. Three others — two journalists and an aid worker — were beheaded by the group.

In each case, their captors demanded huge ransoms, which the United States has refused to pay, saying doing so would only encourage more kidnappings. President Barack Obama has defended that policy, although he has said it was extremely difficult to explain it to victims' families.