Does Jingyi Middle School in Kaifeng only accept girls?

No, according to the Education Bureau of Kaifeng City, official website, the city was renamed Kaifeng No.8 Middle School after a girls' middle school, and students were enrolled for the whole city, regardless of sex. This school is "Kaifeng Model Junior High School" and "Henan University Affiliated Middle School". The school was founded by an American nun in Kaifeng, Henan from 1885 to 1964.