I think it was very on brand for Carrie not to have a go at Miranda for being a big old cheater. For all her many faults she is only judgemental when it comes to what people look/ dress like, she rarely seems bothered by the other girl’s behaviour. The fact she knew Miranda was gaga over Che and forgot to tell her she would be at the school thing was very Carrrie behaviour-does not effect Carrie personally so not an issue. It was funny.