A Dragon's Guide to Making Perfect Wishes, by Laurence Yep and Joanne Ryder (Crown Books for Young Readers, middle grade, March 2017), the third book about an ancient dragon and the girl who is her "pet" (the first being A Dragon's Guide to the Care and Feeding of Humans).
Miss Drake, the dragon, has perhaps grown a little lax with her pet human, Winnie, but it's a laxness born of fondness and indulgence. Miss Drake has known and loved several generations of Winnie's family, and when an invitation arrives to a time travel excursion back to the San Francisco World's Fair of 1915, which Miss Drake visited with Winnie's great-grandfather, Caleb, the dragon decides to take Winnie to meet her ancestor. The time-traveling expedition has its own particular purpose--the magical group of travelers hope to solve the mystery of the theft of the legendary jewel know as the Heart of Kubera. It is no ordinary jewel, as Winnie is about to find out...
The time-travel excursion serves introduce the jewel and its magic, and to simply offer enjoyable time with Miss Drake and Winnie as they explore the Fair. A highlight is their chance meeting with Laura Ingalls Wilder, who was really there*....And this is very pleasant, peaceful time-travel tourism. But there are more plot-ish elements going on at the same time. The Jewel is more than it appears to be (it comes with a wish-granting mongoose component),and there's a villain who wants the jewel and will stop at nothing to get it. The expedition fails to revel the mystery of the theft, and the theft in turn adds a complication to the time travel, in a nicely time-tangled turn of events.
When Winnie ends up in possession of the jewel herself back in the present day, she has to learn pretty quickly how to make wishes that won't make things worse...which is hard to do when she has to make a wish that will save Miss Drake and herself from the clutches of the villain.
A new character, a boy named Rowan with a mysterious identity of his own, is introduced, but mostly this is Winnie and Miss Drake's story. And if you having a difficult sort of week, and just want a magical story about two very different people, dragon and girl, who are very, very, fond of each other, this will be a pleasantly diverting comfort!
*Joanne Ryder edited West From Home, so if anyone has the right to introduce Laura into a time travel book set at this particular World's Fair it is her!