Sounds to me like she had a few champers, forgot about her coat, didnt ask for it, left the plane without it and then remembered too late and now it's someone elses fault.

Sure, of course she is in part responsible - but she told BA within hours of this happening, and it's pretty clear that given that they took the coat from her, they will have known whose coat it was, so it doesn't seem utterly unreasonable that they should have been able to find it. If BA is going to proactively take coats from people, it doesn't seem so reasonable to just throw their hands up in the air if they don't give them back again.

We have tried lost property at the airport (both by phone and on the website) but they're not showing any trace of it. Is there anyone that we could sensibly contact at BA about this?