It would appear that Elizabeth Brown was born about 1776: she was recorded as age 65 in the 1841 census which, as ages were rounded down to quinquennial years, gives 1771-1776 while her age at death in 1847 is recorded as 71 giving 1775/6 (although at the time of death her exact age may not have been known).

There was a baptism at Isleham of an Elizabeth Brown in 1774, two in 1779 and another in 1780. Although the first of these seems the most likely one cannot be certain without further evidence. However, I have assumed it is the correct baptism for going further back in time.