The Old Witch was one of the most flavourful and interesting Khadoran caster. Through MK2, her feat and her signature spell, Unseen Path, were toned down. This basically put her at the bottom of the pile of useful casters, as without these two abilities she has a very lackluster game.
Things that remain powerful in her spell/ability list are Augury, giving Khador jacks the equivalent of Hunter for ranged and melee attacks (good for long range jacks, like Behemoth, Destroyer, and possibly Decimator.) and Murder of Crows (placing that big a template is always good, especially if the enemy has no way around it!)
Things to think about with Old Witch:
1) Needs ranged jacks to properly take advantage of Augury - Behemoth is the first consideration.
2) Has Iron Flesh - possibly the best Khador defense spell. So a nice big unit of infantry is a good idea, either IFP or Assault Kommandos. Winterguard are another option.
3) The only caster with an arc node - good at playing Guerilla Warfare with high threat range spells. Other Guerilla units are a bonus.
Old Witch 35pt list:
Zevanna Agha, the Old Witch of Khador
Iron Fang Pikemen (Leader and 9 Grunts)
Iron Fang Pikemen Officer & Standard
Kossite Woodsmen (Leader and 5 Grunts)
Kossite Woodsmen (Leader and 9 Grunts)Widowmakers (Leader and 3 Grunts)
What ive done here is add the Behemoth for some decent ranged threat, against both infantry and heavies, the Wardog to keep OW safe, a maxed out unit of IFP - these will be my primary force, with the UA, IF and shield wall it should keep them on high DEF and ARM and survivable.
The Widowmakers and Kossites are the Guerilla warfare part of the army, and will serve a harrassment and support killing role. The Kossites will attempt to get behind the enemy and force them to protect artillery/choir etc. The Widowmakers do what they do best, and sniper the enemy.