Here we have a courtesy post for those you with more interest in the dress that Samantha Parkington is using as her Diana Barry costume, which was purchased from Etsy seller Terristouch.
The white pinafore apron has the most wonderful details and is made of a really soft fabric. The other two photos show you just the dress without the pinafore. While there is no real Diana Barry costume like this one from the Anne of Green Gables movie, she does tend to wear white pinafores over a long-sleeve darker color dress to school.