She was born in Linares in 1890 and died in Madrid in 1932. The biography of Isabel runs parallel to that of Antonia López Arista until 1912.
That year Pedro Poveda asked her for special assistance at the Academy of Oviedo, which had started the year before and was the first one in the Work. In this city she competed her Education studies, which had been started in Córdoba. Her name is the second that appears in the first book that listed the members of the Teresian Association. Next to her name one can read that she belonged to the Association “since its foundation.”
With her cousin Antonia in 1908 she started a storeroom for the poor, known in Linares as “The Cradle of the Baby Jesus.” This was a “sewing garage” that gathered a group of young people, led by both, to attend to the needs of many needy families and to foster their faith, based on the writings and thought of the one that a few years later would be the founder of the Teresian Association.
Isabel was gentle and kind. She had a cordial and pleasant personality, a lively intelligence, and exceptional gifts. At the same time she was generous and her availability to the needs of the mission of the Work was truly remarkable.
In 1914 she moved from Oviedo to Madrid, called by Pedro Poveda, to support a University Residence that was started that May for a group of young female university students and students from the Teachers’ School. She also studied there and completed her studies successfully. To those students she was a guide, sister, and teacher; and with Mariana Ruiz Vallecillo and Carmen Cuesta, both young and committed to Poveda’s project like her, she shared in the management of the residence.
Isabel del Castillo was part of the first Council of the Teresian Association in 1916. In 1919 she was appointed Professor in the Teachers’ School in Jaén but in 1922 she took a leave of absence from her work to dedicate herself wholly to the service of the Association. That same year she assumed the responsibility of Vice-Directress of the Teresian Association, the Directress of which was Josefa Segovia. That same year Pedro Poveda left the Administration group that he had shared with them since 1919.
In 1923 she travelled to Rome with Josefa Segovia and Eulalia García Escriche to present the Work to the Holy See and request its Approval. Isabel wrote a journal that describes the entire trip with very specific details about each event. This journal is a real treasure of documentation.
In 1927 she was appointed General Administrator and the following year, in the first General Assembly of the Teresian Association, she made a very interesting presentation on economic issues. In this Assembly she was re-elected Vice-Directress and General Administrator. She died soon after, in 1932, leaving behind an enormous vacuum. Josefa Segovia expressed herself in the following words: “My heart asks me with urgency to speak about her, to continue talking with her and start living like her. It is only justice to always remember who she was for the Work.”.