If you read incognita as disguised, which you should, then the sentence reads:
- Giselle Regan, an American reporter, went in disguised and used hidden cameras.
If that is the intended meaning, then your proofreading question is fine.
The OED gives:
A. adj. Of a female: Unknown or disguised; having one’s identity concealed or unavowed.
B. sb. 1. An unknown or disguised woman or girl; one whose identity is not made known. In 18th c. used often of a sweetheart.
2. Unknown or unavowed character or position (of a woman).
You may recognize this from the famous terra incognita. This is the same word as incognito, just put into the feminine form. The original pronunciation puts the stress on the second syllable, although you will often now hear it stressed on the penult.