I had to look this up. In the book it is "a letter inviting the Duchess to play croquet with the Queen". Now makes me wonder if I have to take a day and power through the book and see if the characters and events in Q's movie match up with the book.
Wasn't the anon with the book. I just looked online for a summary of the chapter posted. I don't know what version that came from.
Found the book. Free on Amazon, but can probably find from another source. https://www.amazon.com/Alices-Adventures-Wonderland-Wisehouse-Classics-ebook/dp/B01BM4XKSQ/ref=sr_1_2?ie=UTF8&qid=1528104040&sr=8-2&keywords=alice+in+wonderland+book