It seems that every time Freud felt he had his successor picked out, the nominee would abandon him.  At least, that's what happened with Jung and Adler.  In the meantime, though, his daughter Anna was attending lectures, going through analysis with her father, and generally moving towards a career as a lay psychoanalyst.  She also became his care-taker after he developed cancer in 1923.  She became at very least her father's symbolic successor.

Ego psychology

Unlike Jung and Adler, she remained faithful to the basic ideas her father developed.  However, she was more interested in the dynamics of the psyche than in its structure, and was particularly fascinated by the place of the ego in all this.  Freud had, after all, spent most of his efforts on the id and the unconscious side of psychic life.  As she rightly pointed out, the ego is the "seat of observation" from which we observe the work of the id and the superego and the unconscious generally, and deserves study in its own right.

She is probably best known for her book The Ego and the Mechanisms of Defense, in which she gives a particularly clear description of how the defenses work, including some special attention to adolescents' use of defenses.  The defenses section of the chapter on Freud in this text is based as much on Anna's work as on Sigmund's.

This focus on the ego began a movement in psychoanalytic circles called ego psychology that today represents, arguably, the majority of Freudians.  It takes Freud's earlier work as a crucial foundation, but extends it into the more ordinary, practical, day-to-day world of the ego.  In this way, Freudian theory can be applied, not only to psychopathology, but to social and developmental issues as well.  Erik Erikson is the best-known example of an ego psychologist.

Child psychology

But Anna Freud was not primarily a theoretician.  Her interests were more practical, and most of her energies were devoted to the analysis of children and adolescents, and to improving that analysis.  Her father, after all, had focused entirely on adult patients.  Although he wrote a great deal about development, it was from the perspectives of these adults.  What do you do with the child, for whom family crises and traumas and fixations are present events, not dim recollections?

First, the relationship of the child to the therapist is different.  The child's parents are still very much a part of his or her life, a part the therapist cannot and should not try to usurp.  But neither can the therapist pretend to be just another child rather than an authority figure.  Anna Freud found that the best way to deal with this "transference problem" was the way that came most naturally:  be a caring adult, not a new playmate, not a substitute parent.  Her approach seems authoritarian by the standards of many modern child therapies, but it might make more sense.

Another problem with analyzing children is that their symbolic abilities are not as advanced as those of adults.  The younger ones, certainly, may have trouble relating their emotional difficulties verbally.  Even older children are less likely than adults to bury their problems under complex symbols.  After all, the child's problems are here-and-now; there hasn't been much time to build up defenses.  So the problems are close to the surface and tend to be expressed in more direct, less symbolic, behavioral and emotional terms.

Most of her contributions to the study of personality come out of her work at the Hamstead Child Therapy Clinic in London, which she helped to set up.  Here, she found that one of the biggest problems was communications among therapists:  Whereas adult problems were communicated by means of traditional labels, children's problems could not be.

Because children's problems are more immediate, she reconceptualized them in terms of the child's movement along a developmental time-line.  A child keeping pace with most of his or her peers in terms of eating behaviors, personal hygiene, play styles, relationships with other children, and so on, could be considered healthy.  When one aspect or another of a child's development seriously lagged behind the rest, the clinician could assume that there was a problem, and could communicate the problem by describing the particular lag.

Research

She also influenced research in Freudian psychology.  She standardized the records for children with diagnostic profiles, encouraged the pooling of observations from multiple analysts, and encouraged long-term studies of development from early childhood through adolescence.  She also led the way in the use of natural experiments, that is, careful analyses of groups of children who suffered from similar disabilities, such as blindness, or early traumas, such as wartime loss of parents.  The common criticism of Freudian psychology as having no empirical basis is true only if "empirical basis" is restricted to laboratory experimentation!

Most of Anna Freud's work is contained within The Writings of Anna Freud, a seven-volume collection of her books and papers, including The Ego and the Mechanisms of Defense and her work on the analysis of children and adolescents.  She is a very good writer, doesn't get too technical in most of her works, and uses many interesting case studies as examples.