Earliest Female Unit?

[Arilian]

. If you have Sprites, for example, you can bet that even in low-level Item Supression battles one of the towers will turn them into sheep...

It is true, also even true for boss fights, but time back is resurrect all units AND dispell the negative spell (often pygmy) AND you can use lvl 1 time back relatively early in the game.
Also you can dispell, and if the enemy control the lake faeries, the sprites can also dispell (this is not often needed but sometimes useful)

Is you have lvl 4-5 units probably it will cast lightning/armageddon killing some from each stack and you have a mutch harder task to resurrect everything.