Dr McMillan trained in General and Respiratory Medicine in London, Edinburgh and Cambridge and completed a PhD during her time at the Royal Brompton Hospital, National Heart and Lung Institute, Imperial Collage London.
She is the lead for the Sleep service, non-invasive ventilation and oxygen and additionally has interests in pleural disease, completing advanced pleural procedures and clinical research contributing to national trials and publications.
She is the East North Hertfordshire NHS trust representative for local primary care clinical commissioning groups and is an executive committee member of the British Sleep Society.