What was Nancy doing on the London Bridge?

Nancy meets Rose and Mr. Brownlow at the bridge. Nancy says that she has had a horrible fear and premonition of death all day, which was why she was too nervous to speak on the bridge. Mr. Brownlow tells Nancy that he believes her story, and that if she leads them to Monks, they will do their best to respect her wishes, and not turn in Fagin or Sikes.