Why postpartum?

I don't mean to sound uneducated. I am honestly just curious. Why is Lindsay Clancy said to have had "postpartum psychosis" when that is condition that occurs much sooner post birth than 8 months?

Could there be another explanation for her reported symptoms? Or is this a rare case of it occurring much later post birth than typical? Or am I simply misunderstanding postpartum psychosis?

Why not just "psychosis?"