You the photo taker. If you feel the girl is in the wrong you can approach her and gently request if she could give up her seat to the elderly around her.
Or the elderlies themselves can wake her up and ask her if she could give her seat up to them if they really need it.
You shouldn’t take pictures and send it to sites to post it up to shame them.
Maybe when she sat down the cabin was empty and she slip into a light sleep and didn’t see the people starting to come in or even if she really is pretending you and other members of the public could have politely ask her if she can give her seat up to others.
You shouldn’t have shame her like this though.
I refuse to join in the rest to insult/scold her.
As I see you having the eyes to see wrong in others but no courage to do something on the spot to change it.
You resort to bitching behind other people back after the incident is over instead.