Nice strategy!
My strategy there (spoiler in white):
I used maximum female troops in army just because of Anya's ring (2 types of spirits, dryads, demonesses). Such army kills everything till the dragons easily. Most important: rings gives +3 init +3 speed (!!!) +3 att +3 deff +3 morale (!!!). Spirits and dryads doesnt recieve retaliation and spirits with such speed going to enemy troops in 1st turn and hit them (just place them in 1st row ). Dryads have mass sleep ability for 1-3 lvl creatures and you can put them in permanent sleep by using "gift" every 2 turns.
Such army works fine even in "impossible".