I485 to my fiance in f1 status

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Hi Gurus ;
I am going to apply the I485 in a week as I got the priority date to current .My question is when can I add my fiance as a dependent to I 485 , I know that Marriage registration is necessary , Is it OK if I apply the dependent 1485 to her before the fingure prints , or I have to apply before the priority date goes back ?

can anyone know what is the best way ?