If you want something done right, do it yourself. The goddess Pallas is the high priestess of… Pallas.
She incarnates as a baby girl and manages to arrange circumstances for her to be raised within or by her own church. She sees firsthand what sort of clergy she has, how devout her congregations are. Pallas herself becomes a priestess, rises through the ranks and becomes her own high priestess. Shen she dies, a new high priestess comes to power while the goddess is born into a new avatar baby girl. She has lead her church though wars, pogroms, an exodus, revivals and golden ages.
No one in her church is aware of this.
In campaigns where gods are as powerful as their worshippers’ belief makes them, she is quite successful. In campaigns where this does not matter, she’s just looking for something to do. Or perhaps her access to the god realms has been blocked.
Would she ever be incarnated as a PC Cleric or Warrior and not know it consciously? Aw, heck no. Please. Your player would be insufferable.