I only decided to insta-kill her because in all likelihood she was an assassin.
You really can't trust mages in the Berserk-verse. Have you read Berserk? They went a couple hundred chapters before finding a friendly mage. Moreover, this one was tracking Guts. The only group that's tracked Guts off the top of my head was the Holy Army that wanted to capture and execute him. The only other major force with clause to track him is the Band of the Hawk.
Secondly, Guts can cleave through magic objects pretty well. The Dragonslayer is antimagic, remember?
You really can't trust mages in the Berserk-verse. Have you read Berserk? They went a couple hundred chapters before finding a friendly mage. Moreover, this one was tracking Guts. The only group that's tracked Guts off the top of my head was the Holy Army that wanted to capture and execute him. The only other major force with clause to track him is the Band of the Hawk.
Secondly, Guts can cleave through magic objects pretty well. The Dragonslayer is antimagic, remember?