The relationship between Circe and Penelope develops into one of understanding and trust. When Circe first shows Penelope her complicated loom, she observes that Penelope “seemed to absorb the loom’s workings by touch alone.” Penelope first sits at the loom after she and Circe have a frank and intimate discussion about their shared history and experiences of cruelty at the hands of others, and Circe learns about the events leading to Penelope being shipwrecked on Aiaia. If “weaving at another woman’s loom is like lying with her husband,” then Circe has effectively shared her bed with Penelope. Sharing a loom is, therefore, an intimate gesture, and it foreshadows how close Circe and Penelope are to become.

Your second question seems to answer itself: Circe trusts Penelope because Penelope has a genuine curiosity for witchcraft. Penelope tells Circe that her pharmaka is “true medicine,” in contrast to the medicines of Odysseus’ palace surgeon which were “only for show.” Circe also trusts Penelope because of the unspoken bond: they have both suffered at the hands of the gods and have the shared trauma of experiencing the private anger of a man who is widely loved and respected. Circe also remembers how Odysseus spoke so fondly of Penelope. Circe’s romantic love for Odysseus transforms to a sisterly love for Penelope, which includes trusting her with her most significant work.

Circe sharing her loom with Penelope is symbolic of an unspoken bond between the two; they are both strong women who have survived trauma, and they have both been in love with the same man. Penelope wants to learn witchcraft because she admires Circe's strength and determination and the very real power of pharmaka. Circe trusts Penelope because her curiosity and admiration is genuine, and she knows about Penelope’s strength and virtue from Odysseus’ lamentations while he was on Aiaia.