
In this new series called Doorways to the Past, Ali Cummings enters, what else?, doorways and is transported back in time. In each book a different doorway leads Ali to the past.
In book 1, Abandoned in Time, Ali meets an old family friend. In 1944. He is a young man during World War II, and Ali must convince him that she is who she is, despite the consequences that will follow.

I hope you get a chance to take a look at these books. They're both free if you have Kindle Unlimited and are just 99 cents to buy.