Jaheira seems to me like someone who could investigate cursed lands.
Druids do try to protect the land and nature, and the Harpens are known for poking their noses into such things.
And the curse looks extremely strong, something like that could leave her temporarily weakened.
Absolutely believable explanation.
OR
She could only be a companion in the camp.
Maybe she could join a mission or two at the end of the game, when your level will be a little closer to hers.
