Before this battle Azra learns Frenzy, one of the best spells in the game. It raises the attack rate of all defenders for a period of time, much useful against the hardest waves. Also, this spell scales: its usefulness remains the same during the whole game, different from Lightning, which becomes obsolete as the opponents' HP gets much higher for the latest levels. It is usual for players to maximize Frenzy and Pushback, another spell that scales well, learned later in the game.
For this battle there are two lanes -- Ketta can be positioned to hit the last half of the way for both lanes. The last three waves are distributed over both lanes. Ketta is probably not strong enough yet to deal with them alone, so you will need help from Slak and any other berserkers you may have.
The Mad Ghoul waves could kill the weakest berserkers, depending on their positioning.