I can't help with the marriages but here's some Hagger baptisms and burials...
Baptisms - Great Hallingbury
18 Nov 1759 - Elizabeth Hagger; dau of Thomas & Martha
22 Feb 1761 - Thomas Hagger; son of Thomas & Martha
15 Aug 1762 - John Hagar; son of Thomas & Martha
14 Apr 1765 - Sarah Hagar; dau of Thomas & Martha
19 Oct 1766 - Matthew Hagar; son of Thomas & Martha
09 Jul 1769 - James Hagar; son of Thomas & Martha
06 Jun 1773 - Newman Hagar; son of Thomas & Martha
04 Nov 1781 - Elizabeth Haggar; base born dau of Elizabeth
Burials - Great Hallingbury
31 Dec 1786 - Newman Haggar; son of Thomas & Martha; age 13
22 Apr 1788 - Nathaniel Haggar; labourer; by a blow in fighting[?]; age 21
30 Jan 1811 - Thomas Haggred?; labourer; age 81 [est b1730]
06 Feb 1814 - Martha Hagger (widow); of Takeley; age 84 [est b1730]
It looks like Elizabeth may have re-married. However, I can't find a burial record for John Russell, nor for Elizabeth Russell.
Marriages - Takeley
05 Nov 1802
William Harwood (x); wid otp
Elizabeth Russel; wid otp
wit: John Pope [?], Mary Savill, Thomas Bird (church clerk); banns
Baptisms - Takeley
16 Mar 1806 - Elizabeth Harwood; dau of William & Elizabeth; born 1st Dec 1805
If this Elizabeth is the daughter of Elizabeth Hagger, then the mother would have been in her mid-forties if she's the same one baptised in Gt. Hallingbury in 1759. This seems quite old so I could be very wrong. I suspect William Harwood was the widower of Rachel Clarke..
Marriages - Stansted Mountfitchet
26 Dec 1769
William Harwood (x); otp
Rachel Clarke; otp
wit: Joseph Ramsey, Thomas Riley; banns
Baptisms - Takeley
05 Jun 1774 - Rachel Hayward; dau of William & Rachel
05 Jan 1777 - James Haward; son of William & Rachel
28 Nov 1779 - William Harwood; son of William & Rachael
05 Jan 1783 - Charles Harwood; son of William & Rachael
11 Sep 1785 - John Hayward; son of William & Rachael; pauper
Burials - Takeley
07 Jan 1800 - Rachael Howard
Edit:
My thinking was that if you can find a burial or death record for Elizabeth Russell or Elizabeth Horwood the age may help determine whether that 1759 baptism is likely right or not.