Final answer:
The sentence requires a comma before the coordinating conjunction 'she' to join the two independent clauses together.
Step-by-step explanation:
The sentence 'Before Ms. Dorsey saw the Bitterroot National Forest ___ she had no idea how stunning the landscape is in Idaho' requires a comma to separate the two clauses. The comma should be placed before the coordinating conjunction 'she' to join the two independent clauses together. The correct sentence would be: 'Before Ms. Dorsey saw the Bitterroot National Forest, she had no idea how stunning the landscape is in Idaho.'