Herja is a tank, the longer she lives the longer she can supercharge your people. Dodge/resist/3 defense runes/HP things like that. Magic won't help her.

Blondie however wants and desperately needs a Magic and hit rune at least, even at lvl 12 she'll still miss more than you'll like but that's just how it is.
The rest of her runes can be normal caster runes. Hope this helps