Rosalind’s main strength is also her weakness. She is telepathic, and this means she can form a closer connection with David. It also means she is hunted by her own people and in danger.
David and Rosalind are part of a small group of people who are able to talk in thought-pictures. This makes them vulnerable.
A few of these looks had been warnings enough to each; it was such looks, not comprehended, but clear enough as signs of disapproval just below the verge of suspicion, that had kept us out of trouble. (ch 4)
However, this is also a strength for Rosalind. For example, when Michael is able to go to a school far away, the other telepaths are able to learn too—including Rosalind.
It was a great satisfaction to learn and know more, it helped to ease one over a lot of puzzling matters (ch 8)
In the end, Rosalind’s greatest strength is that she knows how to depend on others when she needs to. When they are in the Fringes, she is able to communicate her feelings to David when they are apart, and altogether they are able to escape with the help of the Sealanders.
Rosalind is able to keep a clear head and help Petra. Together they can teach her to control her new skills and make sure that all of the telepaths make it to the Fringes. She also helps Petra communicate with Michael and the Sealanders.