That NEHGS database is only on microfilm and is available for use at the NEHGS Research Library, call number F1036.8 .C78 1979
According to my notes Rebecca is listed as arriving at NS with John Bishop in 1760. I will try to locate my source for this. If that is correct, then she must have died by 1761, as John remarried that year.
My notes suggest the 1851 CT death record might be for another person with this name. But that hypothesis is based on her actually travelling to NS with John in 1760.
These notes are edited and originally from GenWeb: "Rebecca supposedly died in New London in 1751. John then married Mrs. Hannah (Allen) Comstock who had lost her husband, Gideon Comstock King George's War (1744-1748). However, Rebecca Bishop/Whipple is listed on the Passenger and Immigration List Index, 1500's - 1900's as accompanying John's party to Horton, Nova Scotia in 1760. In this same Index, another John Bishop is listed as being accompanied by a Hannah (Comstock) Bishop. To make matters even more confusing, John's will (he died on 28 October, 1785) mentions Hannah as his wife"