I can't confirm or deny that Mercy is daughter to Benjamin and Ann Lownsbury.They had a daughter born in 1760.I don't know her first name.She might be your Mercy.The rest of the lineage is correct:
1. Richard Lownsberry b. Broxa, Hackness Parish, Yorkshire, Eng; d. ca Jan. 1690/1 Rye, NY m. 1 Aug. 1670 Rye, NY Elzabeth Pennoyer b. ca 1653
2. John Lownsberry b. ca 1674 Rye, NYd. bet. 1723-1731 Rye, NY d. 1731 m. ca 1702 New Rochelle, NY Anne Guion b. ca 1678 LaRochelle France
3. Samuel Lownsberry b.12/01/1708 Westchester, NY m. 1 Dec. 1728 Hempstead, NY Hannah Carpenter b. 17 Aug 1708 Oyster Bay, Queens Co, NY (dau of Benjamin Carpenter and Mary Coles)
4. Benjamin Lownsbury residing Falls, Bucks Co, PA m. 24 Dec. 1757 Philadelphia PA Ann Young Their children were: ...5. Samuel Lownsbury b. ca 1757 d. bet 1844-1846 He married and had children.the names of spouse and children are not known. ...5. Daughter Lownsbury b. 1 Dec. 1760 ...5. Carpenter Lownsbury b. 23 Jan. 1768 m. Drusilla Smiley ...5.Jonathan Lownsbury d. ca 1609 m. (name of spouse not known) Jonathan's children were Ann Elizabeth b. ca 1797, Mary b. ca 1799, and Benjamin, b. bet 1800-1810 ...5. Elizabeeth Lownsbury b. 17 July 1777 m. Joseph H. Edwards.