It has to do with context. If it is part of a paragraph, and if in the conversation the topic is friends (plural), and a question is asked or the subject breached of her friends (plural), then the answer or sentence addressing the discussion should be within the same logic.
Example:
Bob has lots of friends. Jimmy has a few friends. But Lisa, I think that she says she has no friends.
friends. friends. friends.
"Bob has lots of friends," is a description of how many friends (plural).
"Jimmy has a few friends," is a description of how many friends (plural). The conversation is already about friends (plural), and in this description few could actually be one. But, to keep with the conversation, the plural version is used, and also because of the potential or more than one.
"But Lisa, I think that she says she has no friends," follows or is conversationally aligned inside of the paragraph with a description of how many friends (plural) that a person has. Having used two descriptions that include the plural "friends," has set a precedent of using the plural until the end of the paragraph. It could be set by one use, but for a stronger example you see here two.