I have Permanent Residence by way of a Subclass 866 Protection Visa and I want to sponsor my long term partner. Is it possible to sponsor her and lodge a Subclass 820 Onshore Partner Visa?

You may sponsor your partner however the DHA will significantly prolong processing of a Partner Visa application where the sponsor is a Subclass 866 Visa holder. If your partner is a temporary protection visa holder, they will be unable to lodge a valid application for a Partner Visa, unless the Minister lifts a statutory bar which is automatically imposed on temporary protection visa holders and temporary protection visa applicants. It is highly unlikely the bar will be lifted.