Ding ding ding on Justine. Well done. I couldn't think back that far. She was the last before Kerber (not counting Serena), in 2007. Mauresmo did it in 2006. Venus was 2001. Of course, Serena did it a million times, so that kind of prevented others from having much chance.
I'm torn on whether to say it (a WTA player winning two Slams in a season) hasn't happened much in the last 10 years. Serena 2016, Kerber 2016, Iga 2022, and then Osaka winning back-to-back in 2018/19 and 2021/22... Does that count as rare?
Also, a new Slam champ has been crowned every year since 2014. Ten years. WTA only. I think that will continue.