Rena's mother started her career as a designer at a small clothing manufactory in Okinomiya, where she met Mr. Ryuuguu. They married and lived in a small apartment in Okinomiya until Mrs. Ryuuguu became pregnant; they then moved into Rena's paternal grandmother's house up until Rena started elementary school.

Around this time the manufacturer Mr. and Mrs. Ryuuguu worked for began to have financial difficulties, so she began to consider going independent with a few other designers. The situation became complicated, but she received an offer to work at a design office in Ibaraki and took it. The company promised Mrs. Ryuuguu a responsible project, since the firm had high expectations with her talent. When the family moved, Mr. Ryuuguu had to give up his job and became a homemaker. The project became a large success, and Mrs. Ryuuguu started coming home late every night - some nights she would not even come home due to large projects.

Rena's mother began to take Rena out places without telling her father, including barbecue parties with her coworkers. Around this time Rena's mother had developed an affair with a fellow designer known as Mr. Akihito. She had been drafted by a headhunter to work at a bigger company and was promoted to a higher position, and by this time was earning well into six figures. After taking Rena to a restaurant and eating parfaits with her (Rena's childhood dream), she wanted Rena to leave her father and come live with her and Mr. Akihito. Rena loudly voiced her disapproval, saying that she could continue her relationship with Mr. Akihito but was not allowed to divorce her father. This is when Rena's mother revealed that she was pregnant.

Rena's mother sent a lawyer to the household in Ibaraki many times but refused to meet him in any form, including over the phone. Mr. Ryuuguu became depressed, as did Rena. One day, Rena met with her mother again, but did not speak to her; Mr. Ryuuguu had given her a letter to give to her mother, but her mother did not read it when Rena asked her to. That meeting was the last time Rena's mother met with Rena.

(Source: higurashi.wikia)