I managed to miss the first encounter with her at the Druid grove, so it was a random encounter while exploring. It still felt like a natural progression as a rescue mission, and there are many of those in the game.
Even if you're playing a more neutral or evil party, there is always the lure of XP and loot when completing one of these side quests. Leveling and better gear makes the party stronger for encountering any obstacle along the path to getting rid of the tadpole. As for the urgency of the main plot, I think Larian does a fairly good job in showing through various dialogs that the tadpole is either dormant or aimed at a higher purpose, instead of just a quick transformation.
