She is Yoiko Hibiki. "Yoiko" is actually Ranma pretending to be Ryoga's sister. Ryoga took Akane to his home to see his new puppies, and when Ranma found out, he decided to disguise himself as Ryoga's long lost sister. She's also quite a popular character in Japan. "Yoiko" can be translated as "good girl".
by Samurai Katsu September 15, 2003