Until We Meet Again — Tricia Linden

Victoria Winters doesn't regret her affair at Woodstock, or that she returned from the past pregnant with a daughter who would never know her father. Her only desire is to raise her daughter and live happily ever after, but she's deeply indebted to the Maestro, a mysterious man who saved her life in exchange for ten years of service as his time-traveling courier. Victoria was given a four year hiatus to raise her daughter, but she still has time to pay, and now she's being recalled into service to travel to Manhattan in 1888 to retrieve a lost Stradivarius violin.
The Maestro has tracked the missing violin to Robert Stevenson, a successful investment banker living the good life in the gilded age of Manhattan. After his wife's untimely death he seeks to employ a new governess for his eight year old daughter. When Victoria shows up at his front door it's obvious she's the perfect candidate for the job, even though he suspects there's much more to Miss Winters than she's willing to tell.
If Victoria can find the violin within three weeks, she'll earn extra time off her ten-year contract with the Maestro. If she fails, she risks losing her daughter, and possibly her life. Before her assignment is over, she'll be forced to decide; what is she be willing to lose to have everything she ever wanted?