She died in that room, there were screams & lightening so I’m sure she died.
She also lived which is a paradox so my theory on Ruby stands she simply changed the timeline so she could survive.
As the doctor never went in the room to confirm her death the timline was never set.
I think it’s more likely to be exactly the way she described it:
spoiler
She activated her psychic jewellery to give her combat skills and smacked the shape-stealing alien in the beak with a book.