This is one of those episodes that was so important to the show. Not because it was major plot device but because it was an episode that, for the most part, was random yet hit every viewer right in the heart.
Why did no one remember her?
Does this episode show what humans are capable of or does this show a side of the doctor never witnessed before?
Nobody knew her name because she was just “the hostess”. She was expected to smile and serve drinks… she was part of the whole travel service rather than a person in her own right.
Even when they were all talking to each other to pass the time, and we saw the Doctor having conversations with everyone about their lives and ambitions, she wasn’t involved.
She was just there, even though she was trapped and afraid just like everyone else, but none of them really realised it until she died to save them.