Being a Sitter in the Hall for a time means that Delana was also a high-ranking sister and a strong channeller by Aes Sedai standards. Thus she had the strength needed to use the travel weaves proficiently. This is confirmed by "The Wheel of Time Companion" where her level of strength is described as 18(6). Delana also learned from the Forsaken the weaves and the skill to use compulsion.