Miss Wilberforce is a British lady who is a minor character in the the first book (as well as its television adaptation.). She is the social worker assigned to Dinah Glass and first appears at the start of the series when she is taking Dinah to live with the Hunter family.
She notices that Dinah is acting nervous and tries to reassure her that she has nothing to worry about and that the Hunter family will make her feel welcome. She also comments that Dinah will have to change schools but that she doesn't think that will be much of a problem as she feels Dinah is a clever person.
She next appears towards the end of the book (and the first series) when Mrs Hunter calls her back as she feels that Dinah hasn't really managed to fit into the family as she doesn't seem to get along with Lloyd and Harvey. Lloyd and Harvey, who now get along with Dinah due to them teaming up against the headmaster, beg their Mum to allow Dinah to stay and become there sister and Miss Wilberforce leaves happily.