What std cause pid if not caused by chlamidia or gonorrhoea?

Often unknown: Mycoplasma genitalium is one possibility. However, the exact cause of PID often isn't known. And not all PID is due to STD, sometimes due to entirely normal vaginal bacteria. Also, prior PID sometimes predisposes to repeat PID without known new STD. Diagnosing and treating PID is complex; she needs to rely on the doctor in charge of her care. Good luck!