People don't realise what she goes through on a daily basis... it has a massive impact.
On her ninth birthday, we met Heidi and her mum Cara at the Royal Belfast Hospital for Sick Children in Belfast, Northern Ireland.
Heidi lives with a rare kidney condition, Atypical Haemolytic Uraemic Syndrome (aHUS).
When she was four weeks old, Heidi's family were told that she was extensively brain damaged. She was cared for by consultant Dr O'Connor, who Heidi's family credit for saving her life. Today, Heidi loves sport and, as her mum says, "nothing stops her".