Zerkova is an interesting character - the only true magic orientated Khadoran caster, she is terrible in melee, but has to be close to the front lines for all her spells to be of the most effect. To make matters worse, she is reeeally squishy, 15/15 being rather easy to kill for most heavy jacks with boosts. Even deviated AOEs can hurt her badly.
However, her spell list combined with Arcane Artifacts are quite versatile, powerful and interesting. Highlights are, of course, Watcher, Twister, Razor Wind and Banishing Ward. Watcher wants you to take at least one, if not two powerful Warjacks to make the most of it. You would generally want one Melee bodyguard, and one Ranged or Melee killer. This way you have the most options available to you. A regular Juggernaut or Beast would be good for the bodyguard, and a Destroyer or Decimator would be good for the killer. Banishing Ward can make a unit very good vs certain army builds, like a Cryx magic assassination army. Also prevents stuff like Crippling Grasp ruining your day. I always feel the lack of Iron Flesh really doesnt help Zerkova though.
Twister is cool, Zerkova can produce 4 3" AOEs from between 11.5" - 14.5" away, which scatter if you miss the initial attacks. Although they are low power, they can interrupt enemy movement and attacks. Razor Wind is her staple, and that plus her artifacts should be her main killing attack.
Things to think about with Zerkova:
1) Need good Watcher jacks!
2) Needs a kill condition - she may not be able to perform the kill herself, so needs some backups to get the job done for her.
3) Is not very good with large units, several smaller units is probably a good idea. She requires a toolbox/versatile army.
Zerkova 35pt Army:
Koldun Kommander Aleksandra Zerkova
Battle Mechaniks (Leader and 3 Grunts)
Great Bears of Gallowswood
Greylord Ternion (Leader and 2 Grunts)
Widowmakers (Leader and 3 Grunts)
Winter Guard Mortar Crew (Leader and Grunt)
Basically Ive got some general purpose Jacks to take advantage of Watcher, while bringing along some support in the way of Mortars, Greylords and Mechaniks. My alternate kill conditions (if Zerkova or her Jacks cant get to the enemy) is the Great Bears (with Banishing Ward on them for protection against magic) and the two Manhunters. The Widowmakers job is to harass enemy troops, and the Koldun Lord follows Zerkova and boosts the Jacks with focus, to lessen the load on the caster.
Zerkova advances behind the Jacks, protected by clouds, Twisters and the Wardog, while the support lobs bombs overhead while advancing, and the Great Bears + Manhunters attempt to flank and draw a bead on either enemy Warjacks/Beasts or their caster.