Thank you all so much! That is so interesting!
I didn't know about the 1939 preview. I shall look on it. My hunch is that Kitty (Agnes Kate) was in Severalls by the early 1920s. Their mother died in 1906 when the family lived in Witham. by 1911 they were in Colchester, and the City and County Directory for 1910 shows Frank Crickmore (their father) at 78 Wimpole Road. Then the 1911 Census they are at 64 Winnock Road.
In 1921 their grandmother in Braintree died, then in 1922 brother Bill emigrated to Australia, and in 1923 father Frank followed. My grandmother, Mary, had moved to London with a friend, and I think their other sister Vera was with the housekeeper in Bournemouth. So it is as if the family fell apart. They all kept in touch until they died - apart from Kitty who almost might not have existed. When asked, my grandmother would say things such as: "perhaps she died of a broken heart, dear".
I did try the Essex Health Authority a while ago but they said that records are only kept for 20 years after a person's death.