If it would help I could ask a couple of my nieces for resource suggestions. My youngest great-niece is, I think, a year or so older than Oswin and in a similar situation with being ahead of her age group (her mum is my youngest niece). My eldest niece is a teacher who, for health reasons, had to stop teaching in schools and move to tutoring/home teaching. She trained for primary age range although she now works with a range from 4-18!