First, her quite extraordinary ability to produce children. In the days when there was no recording and all drama had to be transmitted live, performing was a very exacting and terrifying experience. For young children who had never experienced it before, it must have been little short of terrifying. However, Dorothea had the ability to bring out the very best from them. I have seen her extract the most moving performances from children of 12 and 13 who by the time they had been through her exacting rehearsals gave the impression of being highly experienced professionals.
Secondly, since June Averill mentions Prunella Scales's performance as Martha in the second production of The Secret Garden, we should remember who played Martha in the first production. When Dorothea was casting in 1952, she went up to Manchester and interviewed a young girl who had been a child actress in radio drama. This pretty girl had decided to give up acting, but Dorothea persuaded her to defer her retirement and come to London to play Martha. The performance she gave was stunning and made a deep impression on other television producers. But for Dorothea, we should probably never have heard of Billie Whitelaw.