At this point after all six main book and 13 lost file have been published, especially after "The Guard" , we can assumed this person is Lexa - one of three adult Loric escape Lorien on second ship with Ella
... he discovers print copies of a now-defunct newsletter called They
Walk Among Us, a publication I’d been feeding information and funds to
for years ...
- The Guard, Chapter 8
But again, it a bit not so sure about this because
Planet Lorien? The Loric?
7 trailed in Spain.
9 on the run in SA
- I Am Number Four, Chapter 21
Yes she know about first two line, maybe the third too but how she know location(s) of Number 7 and Number 9, since she can't hack to the Mog system (she mention it few time not want to be expose without knowing it) and she don't have the table which can locate the Garde. Or this just another conflict because the author not really done any research of the pre book(s) - another one is when Sarah say Crayton killed in Spain (at Chapter 10) while actually he killed later in India