Unlike Odetta, Detta's personality reappears on numerous occaisions throughout the series, sometimes helping and sometimes hindering Roland Deschain and his Ka-Tet. As is the case when in Blaine's Cradle where Detta solves the riddle of the prime numbers running backwards.
The Drawing of the Three
When Roland Deschain enters the door to 1964 and drags her into Mid-World, Detta Walker is in control and responds in a hostile manner, calling him a "honky mahfah". Odetta Holmes's personality finally wakes up and tries to dismiss the whole incident as a dream, but eventually realizes the reality of the situation and becomes depressed and hysterical. She eventually finds friendship and love in Eddie Dean, another person drawn from her world; however, the relationship is restricted by Detta's personality who hates him utterly.
Detta takes over and escapes when Roland travels through the third door into the mind of Jack Mort. Eddie is left alone in the darkness with Detta, who intends to murder him and Roland. She eventually holds Eddie up with Roland's gun and ties him up in ropes. She leaves him on the beach to get eaten by lobstrosities.
Roland (in Mort's body in Detta's world) realizes a way to save Odetta's life, and brings Mort down to a subway station. He calls for both Odetta and Detta to look into the doorway out of Mort's eyes. When they both look into the doorway, they see each other for the first time and both have combined memories of Mort dropping the brick on their head and then being pushed in front of the train. This has the effect of blending the personalities together, creating Susannah Dean (Susannah as it was both their middle names, and Dean as she is married to Eddie by ka).
The Waste Lands
Detta is summoned again by Sussanah when needed, when Susannah needs to be a little tougher to deal with evil powers such as the demon of the speaking ring, and as in the case when in Blaine's Cradle, Detta solves the riddle of the prime numbers running backwards..
Song of Sussannah
Detta forms an unlikely alliance with Suze when her body is poseed by the demon Mia.