still another angle...
She was sent there by Penny specifically to find Desmond, just the way the guys in the research center also speaking Portugese were working for Penny, too.
Penny doesn't care that Flight 815 crashed. As far as she knows it has nothing to do with the missing boyfriend she's searching for.
Patchy was investigating the flare that Hurley shot and ran smack into them. When Naomi said "I am not alone" I believe she meant, "I'm not the only person who was in the helicopter" as in, "There may be other injured people that came with me that are still alive in the jungle that need help". Patchy would obviously not want the Losties to know this, seeing as he always seems hell bent on not ever helping them unless a gun is pointed at him.
As for Naomi saying "No one survived the crash", she could just be repeating what she'd heard in the news, ad nauseum. I mean, how many transcontinental flights do you know of that have crashed in the middle of the ocean, NOT shortly after take off or while landing? None. That IS the kind of thing that people remember. Hell, I still remember the plane (TWA 800) that crashed off the coast of Long Island back in 1996 and I didn't know anyone that was on it or have any reason to be particularly interested in it. Those kinds of things just have a way of sticking in your head, especially when there's been exhaustive media coverage, as was certainly the case with Flight 815, as witnessed on the monitors that Patchy was watching in his hut.
hm, both of these are great theories, and almost convincing.
i definitely think that she came looking for desmond, and had no idea that flight 815 had crashed there. i also am leaning towards the idea that Mikhail came looking for her because of the flare. he ran in, and walked out with the phone. he was after something.