Why does she have a hyphenated name? I’ve googled her marital status and kept running into a brick wall on the subject. The best I could find was that she has a “partner”. Is she married? Divorced?
It's a new Democrat party requirement.
So it is her mother's married last name.
From Wikipedia:
Spanish naming customs are historical traditions for naming children practised in Spain. According to these customs, a person’s name consists of a given name (simple or composite) followed by two family names (surnames).
The first surname is usually the father’s first surname, and the second the mother’s first surname. In recent years, the order of the surnames can be decided at birth. Often, the practice is to use one given name and the first surname only (e.g. Miguel de Unamuno), with the full name being used in legal, formal, and documentary matters, or for disambiguation when the first surname is very common (e.g. Federico García Lorca or José Luis Rodríguez Zapatero).[1] In these cases, it is common to use only the second surname, as in “Lorca” or “Zapatero”. Note that this does not affect alphabetization: discussions of “Lorca”, the Spanish poet, must be alphabetized in an index under “García Lorca”, never “Lorca”.
More at https://en.wikipedia.org/wiki/Spanish_naming_customs