...it's almost impossible to find a spanish woman's name that does not end in -a.

Haha, so true. I've known a Dulce, a Marisol, a Mercedes, and a Caridad if any of those names appeal to you. What about Josephine? In Spanish it would be Josefina but I know a lot of people tend to Anglicize their names when they move to America. Oooh, what about Soledad? I just looked it up and it means "solitude", which, you know, is pretty apt for a character based on Trowa. XD