In her fifties, Ashdown was the dean of the Shadowhunter Academy when James Herondale came to the school in 1899. She met and adored his father, Will Herondale, and gladly gave the man a tour of the Academy. She later passed on a message to James from Will in Welsh, though she did not understand. The dean was also rather insensitive to and having a hard time accommodating the new warlock teacher Ragnor Fell. When it was revealed that James had the demonic, magical ability to turn into a shadow, James believed that she, like most of the others at the Academy, had also been afraid of him.
- Dean Ashdown married an Ascendant who took on the family name Ashdown, previously held by another Ascendant Sophie Lightwood before her marriage into the Lightwood family.