Legend by Jude Deveraux

Elizabeth Kady Long is 30 years old, an accomplished chef, and engaged to handsome Gregory Norman, her employer's son. While shopping for her wedding, she impulsively buys a large, dusty tin box at an antique shop. When she pries it open, she discovers an 1873 wedding dress and underpinnings, together with a photo of a family. Intrigued, she can't resist trying on the dress, and when she does, she's drawn back into the past. The year is 1873, the place is Legend, Colorado, and Cole Jordan is about to be hanged.