Why do you think Bly's editor told her to describe what she found no matter how positive or negative it may be?

This is because, as a journalist, she owed the public the duty to report the truth free from personal bias or opinions.

Explanation:

Nellie Bly was a famous journalist in the late nineteenth and early twentieth centuries. She was especially known for going under cover or disguising her self, to obtain sensitive information. Her editor at the Newspapers establishment she worked in, encouraged her to write up things as she finds them; good or bad, and to write the truth at all times.

This instruction must have been given as this was a basic requirement for every excellent journalist. Unbiased, true, and accurate reports are among the required and fundamental ethics of the job.

the answer can be "credo" it means to believe = the word credo means "an official statement of beliefs"