When Daniel first goes to their house in Caparnum, Thacia is cool to him, speaking shortly and "turn(ing) on her embroidered sandal and walk(ing) away". Joel is annoyed at his sister's attitude, and tells Daniel she is just "putting on city airs" (Chapter 5).
Later, she tells Daniel directly why she disapproves of him, saying, "If you cared anything about Joel, you would leave him alone. He can be a famous rabbi someday...he's not going to risk his whole future for a band of outlaws". Thacia is afraid that Daniel will lure Joel into following Rosh with him, and if that happens, Joel will lose a future that is lucrative and secure (Chapter 6).
David is totally devoted to Rosh, but Thacia is very much against him, and she tells her brother and Daniel in no uncertain terms, "this Rosh is an outlaw...surely God would not choose a man like that to bring in His kingdom!" (Chapter 7).
Daniel is puzzled as to whether Thacia is for or against him because despite her negativity at times, she is completely supportive of him at others. When Daniel is injured and returns to their house because he has nowhere else to go, she cares for him tenderly and efficiently, bathing his wound and bringing him food and drink until he is well. When he tells her and Joel what happened to his parents, she listens sympathetically and "her eyes (glisten) with tears", and when Daniel and Joel vow to fight to free the country from the Romans, she passionately asks to be included. Once she has made her decision, Thacia clearly demonstrates that she is indeed on Daniel's side. It is she who creates the wording of their vow, citing "the watchword of the Maccabees...for God's Victory", and correctly interpreting the passage in the Song of David from which they draw their identifying signal, the "bow of bronze" (Chapter 7).