Ikoku Nikki

The manga centers on 35-year-old novelist Makio Koudai and her 15-year-old niece Asa, who live together under one roof. Makio took Asa in on a sudden impulse after Asa's parents, which included Makio's older sister, passed away. The next day, Makio returns to her senses and remembers that she does not do well in the company of other people. So begins their daily life, as Makio attempts to acclimate to a roommate, while Asa attempts to get used to an adult that never acts like one.
(Source: Anime News Network)