Bizarrely enough, it might well be a female form of Hercules!
Herklaas is not popular at the moment in South Africa among the Afrikaans-speaking population, but it's a name everyone knows. The short form is Klaas (and the nursery-rhyme character, the Sandman, who helps children go to sleep, is Klaas Vakie in Afrikaans - Snoozy Herc).
The usual female version here is Klasina, but I'm willing to bet that in the Netherlands they'd use Klaaske or Klaasje. Perhaps also in the parts of Germany close to the Low Countries.