I also checked on Ephraims siblings to see if they had any daughters named Mary born at that time and they didnt.
Only female born around that time in this line is:
Nathaniel the brother of the Ephraim I referred to in my other post had a daughter:
Elizabeth b. 14 Apr 1745 Mansfield, Coventry Co., CT d. 1831 at Mansfield aged 87. Her will dated 30 Mar 1827, proved 7 Dec 1831, bequeaths to Adolphus and Elizabeth (Kidder) Smead, the use and occupancy for life of land in Mansfield, originally belonging to her grandfather, James Kidder.
dont know if any helps...