The law only says teachers must come from a native English-speaking country, the big 5: Canada, UK, USA, South Africa and Australia. Twenty yuan says this requirement isn’t from Chinese people, it’s for some school for children of racist diplomats. Beijing is just the worst.
Because that’s where the fortune 500 companies, journalists and diplomats are and they only want “the best” for their kids. That’s why it specifies female. Chinese just want native speakers, sometimes white but usually they’re too cheap to bother. Plus you notice over time the worst foreigners in China are always in Beijing. They think the entirety of China exists within the fifth ring road. I’ve met people who’ve lived in the English bubble for 10-12 years and barely speak 100 words of Chinese, mostly having to do with ordering beer.