As mentioned by krazer in the comment, she is Yuki Uchiki. She is finally introduced in episode 10 Chewy, Melty. (Japanese title: Hamohamo, Michichi.) when Kirin eavesdropped on her phone conversation and accidentally fell (and safely landed) on her veranda.
In the anime, episode 10 happened around January (as the next episode happened in February, and the previous episode happened on New Year's Eve). At this time, Yuki was a graduating undergraduate student, while Ryou and Kirin were preparing for their high school entrance exam in March. According to her wiki page on nicovideo, she is going to work as a librarian at the same high school where Ryou and Kirin goes to.