There are no sources attached to Samuel Knightley, Elizabeth's father, just a possible date of birth, 1702, so this is what the OP has to investigate in order to find a possible cousin baptised c. 1736.
EDIT: I have updated their trees on FamilySearch, giving the fact that the two marriages and all their offspring were attached to the same Elizabeth Keightley and it's clear that there were two Elizabeth Keightley, otherwise the system doesn't search for possible matches.
These are the IDs:
Elizabeth Keightley P723-Q4Z. (married to Robert Potter and died in 1799)
Elizabeth Keightley LVLN-X91 (married to Samuel Orringe and died in 1789)
Of course this can be changed, but so far the system has accepted the new arrangement.