Hidden in Time. The After Cilmeri Series, #17

When Meg time traveled to 1268 Wales and landed in the arms of Prince Llywelyn, she changed the course of history forever. For most citizens of Earth Two, those changes were for the better, but one family in particular was torn apart . Orphaned since the death of her parents when she was three, Lizzie has spent years praying for someone to rescue her and her sisters from a life of drudgery in their isolated convent.
She knows they were meant for greater things, and if only the right person were to discover their suffering, they would once again be treated like the princesses they were born to be. But when strangers arrive in the middle of the night promising to restore them to their former way of life, Lizzie surprises herself not only by running away, but by turning for help to the very person who'd ruined her life in the first place: Queen Marged of Wales. It just went to show, as Lizzie's old abbess told her more than once, that she needed to be careful what she prayed for.
God answered every prayer, but sometimes that answer was no-and sometimes the answer came in a wholly unexpected fashion that made a girl wish she'd never prayed at all. Complete Series reading order: Daughter of Time, Footsteps in Time, Winds of Time, Prince of Time, Crossroads in Time, Children of Time, Exiles in Time, Castaways in Time, Ashes of Time, Warden of Time, Guardians of Time, Masters of Time, Outpost in Time, Shades of Time, Champions of Time, Refuge in Time, Unbroken in Time, Outcasts in Time, Hidden in Time, Legacy of Time, Renegades in Time.
Also, This Small Corner of Time: The After Cilmeri Series Companion.