In the hit Channel 4 sitcom, four-year-old Zoe Brown plays Anna Quinn, Erin Quinn’s younger sister.
The drama follows four young Derry girls and their English cousin as they grow up in Northern Ireland during the Troubles and the Good Friday Agreement, which ended earlier this year.
Zoe, who co-starred with her twin sister Sophie as Anna, was diagnosed with leukemia seven weeks ago after her mother noticed she was pale and rushed her to the hospital.
The youngster has since had extensive chemotherapy and other therapies, including many bone marrow biopsies.
Despite this, Leah Brown, Zoe’s mother, claims she’s still smiling. ‘I guess I was just in a daze, to be honest, I still am,’ she told Belfast Live.
‘She’s been in theatre so many times, she gets lumbar punctures to put chemo in her spinal fluid as well and that’s done under anaesthetic.
‘You never think your child is going to be in theatre at all and the last seven weeks, she has been in loads of times.’
Derry Girls creator Lisa McGee said she had been saddened to hear about Zoe’s poor health.
She told the website: ‘I am so sorry Zoe is going through this, She’s the most wonderful little girl and we are lucky to have her as part of our Derry Girls family.’
According to the website, Leah, who works for a mortgage company, has had to leave her job to care for Zoe while she undergoes therapy.
Zoe will need intensive treatment until Christmas, followed by two years of maintenance chemotherapy.
A family friend has organized a fundraiser to assist with the family’s expenses.
‘I’m really overwhelmed by everyone’s kindness and support, everyone has been so nice and willing to help,’ Leah explained.
‘It’s just unbelievable, people are just amazing, they really, really are.
Meanwhile, a JustGiving page, set up by Shelley Smyth, has described the ‘brutal’ side effects of Zoe’s drugs.
On the page, it says: ‘Zoe got a diagnosis in May that she has acute lymphoblastic leukaemia.
‘It all happened so fast, she has had three blood transfusions then has had a bone marrow biopsy. Her treatment includes lots of different chemotherapy drugs.
‘The side affects of all these drugs are brutal, she can barely walk at the minute and has lost all her hair.
‘It’s a long road ahead so with the help of our community we can all come together and do what we can to help the family.’
The JustGiving page aimed to raise £500 but has since raised more than £4,000. The family are also planning a fundraising event in Belfast.