Mrs Ikaruga is the wife of Hoji Ikaruga.
10 years ago, she wore a kimono and had short hair parted in middle. Later when Sayo Ikaruga was older, she appeared to wear a black shirt and her short hair is with bangs. (It's unknown whether the two appearances are the same person, though)
In another flashback of earlier time, she asked Shimon that if he was alright, for Shimon didn't have the appetite, thinking about Tenma Unomiya.