Unfortunately, we cannot do look ups for the 1911 census due to copyright restrictions.Sandra
Have you checked that she isn't with any other members of the family?
The other possibility is that she's in hospital under just her initials. Although as Elizabeth is only 14 she should be somewhere.
I am trying to find Kate (Catherine/Katherine),Elizabeth,Charlotte (prob married) and George.Kate died in 1926,Elizabeth and George-no idea.