Eilidh MacLeod from Barra was among 22 people who died in the blast at an Ariana Grande concert two weeks ago. Dozens of others were injured.
Speaking ahead of the ceremony at 11.15am inside Church of Our Lady, Star of the Sea in Castlebay, local priest Fr John Paul McKinnon said: "She was an island girl, she was proud of her island roots and a fun loving, good girl.
"She's that wee ray of light that will never go out."
The 14 year old's friend and fellow pupil at Castlebay Community School, Laura MacIntyre, remains in hospitals after being seriously injured in the suicide bombing.
Eilidh's parents, Roddy and Marion, said: "Two weeks ago today we lost our darling daughter and sister, Eilidh MacLeod, in one of the cruellest ways possible.
"Most of Eilidh's happiest times were spent in the Western Isles, particularly Barra and Vatersay, with her friends and family so we are pleased to have her back home among those she loved so much.
"Today, as we take Eilidh on her final journey, our one hope is that her funeral is a real celebration of her life and the wonderful person she was."
The funeral will be attended by several Scottish ministers. Businesses on Barra are expected to close for some hours on Monday so workers on the island can also pay their respects.
Roddy and Marion went on to say: "Eilidh's infectious personality touched everyone she met and it has been a privilege and an honour to have her as our daughter.
"We will always remember her as a truly beautiful girl inside and out, eternally young, loved by all and forever in our hearts."