Kett Cardinal is one of the most powerful enemies found in Mass Effect: Andromeda. You'll encounter her on Voeld after a short pursuit through the Kett outpost whose exploration is one of the objectives of A Trail of Hope, a storyline quest found in the game.
The battle can be challenging, as your enemy is quite powerful, and has a very unpleasant ability - the Cardinal can catch your hero and transform him into a Kett, which ends the game permanently, forcing you to reload your last saved game. Fortunately, in most cases you can escape her clutches by making a timely dodge when located in the near vicinity of the enemy. To avoid the attack completely, stay away from the enemy and attack him from a distance.
The Cardinal can also send energy spheres (such as the one shown on the screenshot above) that erupts and grows in size before dissolving. If you got caught in its radius you can lose your shield and additional health points. The area of the encounter is large and varied, so you should always be able to clear out from the blast zone.
Your enemy is an ascendant, surrounded by a force field that makes your attacks inefficient. Avoid shooting directly at the shield and focus your fire on a small orb floating around your opponent.
Once you've destroyed the orb, start firing at the Cardinal, but be swift, as your enemy will be vulnerable only for a short amount of time. Use your best weapons and most powerful abilities to gain the most from the window. Finally, the shield will come back online, and a new orb will appear. Repeat the process until you've managed to eliminate the enemy.
You'll also have to deal with Kett troopers that should be eliminated in the first place. Unfortunately, a new group of kett appears every time you've took a portion of the boss' health (1/3 and 2/3 of his health bar). Do not ignore the reinforcements, as the group includes Destined and other elite units. Switch your focus on the incoming troops and then return to engaging the cardinal.
The battle can take even up to a few minutes, especially if you've chosen one of the higher difficulty levels. Additionally, use the supply crates lying around the area to replenish your ammo and biotic powers.