The question is, how did the Chinese immigration know? for each applicant do select count(*) from people_who_pissed_us where social_username = applicant.fb.username?
It's not that hard. When you apply for a visa you must state if you're a journalist or not. After that, a quick Google should suffice, especially if the articles written by her became popular.
After switching of The Great Firewall for ones own browser, that pesky thing blocks useful information.