Ever since experiencing the Lumiose ghost girl's first and last appearance, lots of people including me have been searching all over Kalos and the internet for theories on what her appearance means. I have heard of many theories and have actually started to come up with one. Post your theories/thoughts here.

Here is my theory. I have searched all over the internet and no one has pointed out what I think is a huge possibility for the ghost girl.
So, as you all know, the ghost girl shows up once, on the second floor of a building in Lumiose. She has the appearance of the hex girl NPC. There is a blackout, the music goes away, and the girl appears behind you. She moves, legs strangely positioned and not moving, and says, "No, you're not the one..." After that she never shows up again, and the room is just a normal room. On the 4th floor of Hotel Richissime there is a girl (once again hex girl NPC) in the room. She is in the left side of the room, and across the wall is the elevator. She says, "... ... ... ...Don't talk to me... ...If you do, I won't... ...hear the elevator..." This is strange because the girl in the other building seemed to be waiting by an elevator, too, but it's strange because this girl is...alive. Is she possessed? A completely different person? No one knows.

In the Lumiose Station, there are two billboards; go to the one in the back. Press A while standing behind it and you will be told that "Something is written on the back of the timetable: I'm going to go for help. Wait in the usual place". What does the message mean, and why is it here? Obviously whoever wrote it didn't want just anyone to see, so it was put somewhere where people wouldn't normally look. But who's the message from or for, and why do these people need help? Where is the usual place? It makes no sense. Nearby a little boy says, "It should be someplace right around here, right?" Lots of people believe that the little boy saw the note and is also looking around. But...I still wonder what "help" was needed. What if the help didn't get there in time? Did this cause the girl to die, and is she still waiting for that person? Waiting by an elevator...is a certain elevator the usual waiting place? And why where there two girls waiting by two different elevators? Was the message unclear and she didn't know which one? Hmmmmmmm.......

HERE IS THE PART THAT I THINK NO ONE HAS FOUND OUT YET!!!!!!!!
Why is the message at Lumoise Station, of all places? This made me think. I concluded a theory of my own: The girl lived in Kiloude City. This ghost story has to do with Hoopa.
A bit out there, yes, BUT!!! Go to Kiloude City and enter the first house after the station. Seriously, I flinched when I saw yet another hex girl NPC. She gives you the move Petal Blizzard and seems really cheery. But it's weird because all the other hex girls in the game aren't usually so happy, and instead more on the strange side. This girl is the only person in the house. There are two beds. Who slept in the other bed? I know that all the houses in Kiloude City have this same layout and furniture, but the game designers could have simply put another NPC in the house, saying whatever random quote. But no, this girl is all alone in the house; did the ghost girl use to live there, too? In this house? Again, I know that this is really out there, but it's a good step further into the mystery!
The reason for the message being at Lumiose Station is possibly because the girl was traveling from Kiloude City by train; trying to investigate or solve whatever this other person went to get help for. After (somehow, lol) finding the note, she went to "wait at the usual place" for the person to arrive with help. But as I said earlier, why are there two girls waiting at two different elevators? The help and the other person obviously never came back if she's still waiting...and everything seems normal. What is she so concerned about that she needs to wait for all this time? I believe this all has to do with Hoopa. I know that this is a bit out there too. But Hoopa is a Ghost/Psychic-type and hex girls usually use Ghost-type and/or Psychic-type Pokémon. Hoopa may be the "help" needed, and because it is a mysterious and (apparently) legendary Pokémon, the hex girl decided to wait, even after she had died, for it to come to her. Whatever the problem, this is obviously a big deal for her and the other person.

Well, there's my theory! I'm sorry if it's stupid...I don't usually explore this much into the game's possibilities. xD
But I believe everyone's theories are important, for any one of them could be true. Every idea is a step closer to figuring this all out!
Thank you everyone, please comment your thoughts or theories below!