Dolores doesn't speak much in Castlevania: Order of Shadows, but she is equally capable of handling the Vampire Killer. She's just not of age yet.
Dolores, while not playable, helps Desmond along the way-they also make it easier to avoid having the main character talk to himself constantly.
Some fans speculate that Zoe and Dolores's name is inspired by another Konami game Z.O.E. and a character form Z.O.E. Dolores,i, a related animation, respectively, although the these two names are very common.