The Northants Indexes do not appear to hold a baptism for an Elizabeth Jackson around that time to parents Richard & Mary ... the closest is 1774 in Weldon, and checking the registers I have no reason to believe this to be a late baptism. Her parents, Richard Jackson & Mary Malsher, married in Weldon in 1766 and their first child Richard was baptised the following year.
Neither is there a marriage for a Mary Voce.
Where did "Northamptonshire" come from, please?