The Magic Half
by Annie Barrows is reduced to $0.48 (US Kindle)
Miri is the non-twin child in a family with two sets of them--older brothers and younger sisters. The family has just moved to an old farmhouse in a new town, where the only good thing seems to be Miri's ten-sided attic bedroom. But when Miri gets sent to her room after accidentally bashing her big brother on the head with a shovel, she finds herself in the same room . . . only not quite.
Without meaning to, she has found a way to travel back in time to 1935 where she discovers Molly, a girl her own age very much in need of a loving family.
A highly satisfying classic-in-the-making full of spine-tingling moments, this is a delightful time-travel novel for the whole family.