Rhiow isn't joking when she calls Antonio "cousin" - they both do the same thing, in very different ways. He's another one that she wishes would be offered wizardry, even though he's too old to still be in latency as well.

His fears during the Nightmare King of falling to the evils in his world rang very true with her. At some point every wizard has to face the awful temptation of giving up their Mastery, or giving it over to the Lone One. Seeing him face that down with her help gave her courage. The fact that he honors the Powers (even if he does call them spirits) also makes her happy - it's good to have a kindred spirit on board.