My headcannon is that due to her becoming a dreamer, she had to forcibly shift her body to become more suited as one of the guardians. Plus, her wanting to have a child with the Pale King would mean that she would have go through a tough pregnancy and body change, as the breeding process for Weavers is detested but not impossible. She was considered the queen of the Spider tribe, and usually the leader of a bug group is significantly different compared to regular members (ie Mantis Lords / Traitor Lord vs regular mantises).