Hi , as per your info she is on anticoagulants The need did one after covid infection depends on the condition and markers when she had active infection , if she has comorbidity like diabetes hypertension or heart disease preferably it’s better to take it for 2 month or more D dimer values may not be a good indicator to stop But agin depends how much her d dimer values were initially

Needs blood thinners to prevent clot formation as D-dimer levels are high

Till 28th day of illness should be count from the day first symptom appear..

600 is too high..continue Rivaban for two weeks and do repeat d dimer test.