Susan is very good at not making facial expressions, and furthermore has prepared for many people at Galahad's party liking the boy who he asked to sort out the entire affair, so her mouth doesn't thin at the mention of Magnus. "I'm afraid I haven't got any sense of when he's from," she says, an explanation for how this doesn't clarify the full extent of Lan Wangji's meaning. It's merely clear he's from her future, as well.