Why was Sacajawea inporten to the Lewis and Clark journey?

Sacajawea was invaluable as a guide in the region of her birth, near the Three Forks of the Missouri, and as a interpreter between the expedition and her tribe when the expedition reached that area. After she gave birth during the expedition to Jean-Baptiste Charbonneau on February 11, 1805, she also quieted the fears of other Native Americans, for no war party traveled with a woman and a small baby.