Adin knew that he was the one who must fill the medallions in the belt.
Sisely is in need of more information! Sisely is lacking a personality section. We don't know a lot about Sisely and Lenah, so simply summarise anything we do know.
"I circled “Determination”. But I am sure it was wrong. Oh, and some of those word questions were very hard, Lenah! Is “currant” the pull of the tide, and “current” the dried fruit? Or is it the other way round?"
— Sisely to Lenah
After completing the preliminary test, the candidates in the Rosalyn Trust competition, amongst was Sisely, were lead by Trader Sorrel to the Traders' Hall luncheon room. On their way through a broad hallway lined with objects that were part of Del's trading history, Sisely's friend Lenah asked her what she had chosen as a good trader's most important quality — she herself had circled "Confidence". Sisely had circled "Determination", but complained that she was likely wrong.
Sisely told Lenah that she had found some of the word questions of the test hard. She was not sure if "currant" was the pull of the tide, and "current" the dried fruit or the other way around. Another candidate, Vashti, walking in front of the pair, glanced over her shoulder to correct Sisely, saying that the fruit ends in "ant", and that it was easy to remember, as long as you just think "that ants like currants, but don't like water." nah thought without a doubt that Vashti had had everything right and Sisely could not even think of why the rest of the candidates even bothered to come, since everyone expected Vashti to win in the end. Sisely had tried to tell her mother, but she had insisted on her competing. Lenah reminded Sisely there were to be three finalists, but agreed that Vashti would be one of them, however mischievously she added that no one knew what might happen to the girl on the trial voyage; she suggested that Vashti might fall overboard and drown, or even worse. She jerked her head towards a framed letter on the wall penned by the famous Mikah in his own blood, telling of the gruesome quest for the Staff of Tier that had ended in blood and horror, with him steering the Star of Deltora home from the Isle of Tier to Del harbour while mortally wounded. Sisely, spluttering with laughter, hushed Lenah. Smothering their giggles, the girls moved on..
Sisely is smartly dressed, as would be expected of a trader's daughter. 
As she is a trader's daughter, it can be assumed that Sisely has some sort of skill in trading.
Lenah appears to have a close friendship with Sisely.