That's what she said is used when someone says something dirty without intending it to sound like that. You have to have a dirty mind to get them.
Kate: Ah, I'm all wet now and it's all your fault!!!
Hayley: Ew! That's what she said!
Kate: Gross! I meant your hose soaked me!
Hayley: That's what she said again! Haha, you're making things worse for yourself now!