Answer:
Siobhan is encouraging to Christopher and enjoy talking with Christopher. The parents are mostly discouraging to Christopher, but this is seems not true in that they need to provide for him on daily bases. This pattern is similar for many of us 'normal' people (parents seem to be discouraging while others seem more encouraging.)
Step-by-step explanation:
Christopher often mentions Siobhan when describing the aspects of human communication with which he has trouble. We assume it's through her that he's at least learned how to be polite and found out about this strange way of talking called "chatting." But our favorite Siobhan moment is when she reads Christopher's detecting book and offers to talk to him if he's feeling sad about what he's learning about his mother.