According to my great-grandmother's writings, after Mr. Lockwood's first wife died, Mary went to work for him as a housekeeper, and he later married her.
In the 1900 Federal Census, Mary and her husband Abraham Lockwood are living in Warwick, RI. She is age 65 and he is 68. They have been married for 8 years. According to the census data, Mary immigrated in 1847.
Abraham & Mary are still at Warwick in the census taken 27 Apr 1910, although Mary must have died shortly after this.
Note from RI Historical Cemetery Database: born ENGLAND; Swan Point Cemetery, removed 7/15/10 to Warwick, RI; cause of death: Heart Disease died: WARWICK,RI