Dr. Castell completed her Higher Specialist Training (CCST) in Family Medicine in Spain in 2002. She became a Specialist in Occupational Heath Medicine in 2006 and was awarded her MD by the University of Las Palmas in Spain.
From 2007 to 2009 she worked for Custom House Square Medical Centre in Dublin. She subsequently returned to Spain where she worked for 6 years in a Primary Healthcare Centre as a GP and GP tutor. During this period, she lead the national programme for tobacco and alcohol abuse and a joint injection programme.
Dr. Castell was appointed UCD Clinical Tutor upon returning to Ireland in 2014 . In 2015, she rejoined Custom House Square Medical Centre as Medical Director.
She played a leading role establishing Point of Care Ultrasound in General Practice in Ireland in association with the ICGP. In 2018 Dr Castell completed a certificate in Obstetric Ultrasound in UCD School of Medicine (University College Dublin)