Samitische Kräuterkundlerin

If Samite Herbalist becomes tapped while casting a spell or activating an ability, that spell or ability resolves after Samite Herbalist’s triggered ability has resolved.

Samite Herbalist’s ability is a triggered ability, not an activated ability. It doesn’t allow you to tap it whenever you want; rather, you need some other way of tapping it, such as by attacking.