Erika was a deceitful captain of the Evil Horde, who hated the Great Rebellion for killing her parents. You are He-Man, the hero of Eternia the Great Rebellion, you show her that it was the Evil Horde who killed her parents, and she left her position as captain to be a Rebel.

"Hordak will pay for deceiving me" she says as he walks with you, but then she looks at you and smiles "Thank you for showing me the truth and opening my eyes to reality"