i'm sorry to say that but there are 2 mistakes in your understanding.first ,她 means she/her.yes this is a girl.second, 衣服穿脏了不洗，就反过来再穿means“when her clothes become so dirty, she turns them inside out and continues to wear them instead of washing them".

我真受不了她，衣服穿脏了不洗，就反过来再穿。 I can’t stand him anymore because he wears dirty clothes inside out which should be washed

In fact this sentence will be much easier to comprehend if you insert a character in front of 不洗： 衣服穿脏了（还/也）不洗 (Even if) she wears clothes until they are dirty, she still won't wash them. And there is also another commonly used structure 不+v1+就+v2 which means “do sth. without doing sth. first". For example: 不带钥匙就出门 - go out without bringing keys 不洗手就吃饭 - have meals without washing hands so 不洗，就反过来再穿 means "turn them inside out and continue to wear them without washing them" Also please notice that 她 means "she", not "he". Hope it helps :)

衣服穿脏了不洗means (although)the clothes are dirty ,he is not going to wash them.

"她“ means ”she " the clothes are dirty, but she still not wash them, she just turns them inside out and continues to wear them." Sorry, my english is not that well, Hope that above explainations are helpful for you.