Marcella, who is in year 9 at Aylesbury High school has decided to 'Brave the Shave' to raise money for Macmillan Cancer.
Marcellas Mum said: "She is 14 years old and has lovely long hair so my husband and I are a bit nervous that she has decided to shave it all off (Yikes!!) but we are incredibly proud of her for her determination to do this for such a worthy cause.
You can donate to the cause here: https://bravetheshave.macmillan.org.uk/shavers/marcella-just
Marcella said: "My mum's Auntie Molly passed away from breast cancer before I was born but I have heard a lot about her over the years.
"She was my Grammy's identical twin sister and so would have been a close family connection had she lived. It makes me sad that I have never met her. Also, unfortunately, my Grammy has been diagnosed with a slow growing cancer.
"Recently my mum's university friend shaved her head in support of cancer in memory of her mum and she inspired me so much that I want to do the same. Cancer is such a horrible disease and no one deserves to suffer like that so I want to sacrifice my hair to help those that really need it by raising money for Macmillan.
"Although I do like my hair, helping people with cancer is much more important to me. I am also going to donate my hair to the Princess Trust to be made into a wig for others who have lost their hair as a result of life saving cancer treatments."
Her mum added: "Everyone is so impressed that a girl of her age is willing to shave all her long hair off at a time in teenage girls lives where image is normally considered to be quite crucial to their self esteem.
"I personally think this shows a great message to teenage girls and people in general that it is what is inside you that counts and not what you look like that is so important.
"Hopefully it will help people with self esteem issues to value their inner qualities of kindness more than their looks and help society in general to realise this.
"Marcella has an incredible attitude to shaving her hair off and is confident in herself that it will grow back and not affect her life or self esteem but what is important to her is to raise as much money as she possibly can for cancer as her life and nearly everyone out there's lives has been affected by cancer in some way. It has touched all of our lives."