Answer:
" the badge issued to her by the newspaper "
Step-by-step explanation:
The best and simple definition of the word "credentials" is "any piece of document that contains information about a person and his/ her qualification. This means that the document acts as permission to be eligible to do a certain thing.
In the given passage, the woman works for a certain newspaper. But she wasn't allowed entry as she lost her 'entry pass'. This entry pass is in the form of a badge that press members are issued with. So, the 'credential' for her is the 'badge' that signifies that she's qualified to be inside the press conference room.
Thus, the phrase that provides the best clue to the meaning of credentials is "the badge issued to her by the newspaper".