Pallas was Athena's old friend back on Earth. Pallas is a mortal, and is featured only in the books Athena The Brain and Pallas The Pal. However in the mythology, Pallas is the daughter of Triton and is a nymph. As such, no excess information of Pallas was revealed in Athena The Brain.
Pallas was a helpful friend who is very protective over her and Athena's friendship, for example, before Athena left, she made Athena promise to never forget her. She is a loyal friend and who is very supportive. She supported Zeus' idea for his daughter to go and live on Mount Olympus.