Is Yae Miko the Previous Electro Archon?

Yae is not the previous Electro Archon.

Who was the previous Electro Archon?

Baal refers to the previous Electro Archon, who was in power 500 years prior to the current story. She perished during the destruction of Khaenri'ah. You might also know the event as the great cataclysm. Baal was the twin sister of the current Electro Archon.

Is Yae Miko Baal?

Yae Miko is stated to be an “old friend” of Baal and is one of her most trusted allies.