Lady Eresh joins the Knight Revenant faction as an all out damage dealer. She is part of the free champion reward chain you begin after you complete you 270 days reward track and can be earned after you earn Guurda Bogbrew (although you will likely pull her before you receive her for free).
Her only role is deal damage and unfortunately her multipliers are not top tier so she joins a number of epics in the “what could have been” category. She buffs herself with an Increase Attack and Critical Damage buff then granting an Extra Turn. She then unleashes an AOE attack which can grant an extra turn. If enemies live and she does not get an extra turn she will instead gain turn meter based on remaining enemies. Its unlikely you can rely on her extra turn to finish off any targets at such a low chance.
If you pull her early, she will serve you well as a mid game or Low to Mid Gold Tier arena nuker but she will not able to hit hard enough for top tier arena.