Anyohe know the name of this book?

[Linn]

I've been searching for this book I read as a child that's about a girl named Lydia who encounters a boy that looks like a bird. The bird boy gives her pills that make her capable of speaking every language in the world, with the purpose of sending her back in time through touching paintings, which brings her to when the painting was created. Lydia was forced to buy up paintings cheaply from now world-famous artists before they were well known, which led to a huge commotion in real-time since famous paintings suddenly disappeared. Lydia realized she was stuck in time since she could only travel backward (because all existing paintings were created before the current moment), but she's eventually able to return to her own time by painting her own painting. There was a sequel as well, where Lydia keeps seeing the same tiger when she jumps through time and meets Diego Rivera and Robinson Crusoe, just to name a few. It's been driving me crazy that I've been unable to find the book, so please tell me if you know the title :)