Brown, who is four, appeared in the Channel 4 sitcom as Baby Anna, the younger sister of lead character Erin (Saoirse-Monica Jackson).
She shared the role with her twin, Sophie, in the second and third series of the show.
Speaking to Belfast Live, Zoe’s mother Leah revealed that she has undergone chemotherapy as well as numerous bone marrow biopsies and lumbar punctures.
Leah says that losing her hair has been “the saddest wee bit” for her daughter and that, even though she is currently unable to walk due to side effects of the treatment, she is “still smiling”.
She said she has given up work in order to care for Zoe as she undergoes her treatment, which will last until Christmas. Zoe will also need maintenance chemotherapy for another two years
Leah said that Zoe’s sister has started primary school without her.
A JustGiving fundraiser page has been set up by a family friend in order to raise money for costs, with Derry Girls creator Lisa McGee sharing it online. Find the page here.
McGee said she was “so sorry” to hear of Brown’s sickness, and called her “the most wonderful little girl”.