As yet I can find no sourced records of birth/baptism of Anne Waghorn, however her daughter Caroline Ouzman was buried in the grave of Anne's parents Wiiliam and Mary.
Grave Inscription:
In memory of Mr. William Waghorn of this Parish, bricklayer who died 26 Sept. 1771, aged 48. Also Mrs. Mary Waghorn widow of the above, who died 16 Sept. 1800, aged 70. Mrs. Susannah Waghorn daughter (in-law) of the above died 23 June, 1800, aged 33. Caroline OUZMAN grandchild of the above died 11 April, 1802 aged 5 years.
I was somewhat confused when I looked at this, Nick. Having a quick look at all the family profiles I think you are incorrectly saying it is Mary Waghorn you are having the problem with, when it should be Anne (Waghorn) Ouzman. Anne's profile even starts out saying "As yet there are no sourced records of birth/baptism of Mary Waghorn". So, looking at Anne, I can see there is a baptism for an Anne Waghorn at Blenchley in 1751. However, that Anne was the daughter of Samuel Waghorn. Therefore, I ask you: How do you know that Anne was born about 1751? How do you know that Anne was born at Bletchley, Kent? These are especially pertinent because you have WIlliam Waghorn marrying Mary Ray in 1753 in Croydon, Surrey, and you have Mary and Sarah baptized at Croydon, Surrey, in 1754 and 1756 respectively, with John baptized at Lewisham, Kent, in 1760. You might also note that there is a William Waghorn baptized 1758 at Dulwich, son of William and Mary. He might fit into that gap in 1758 between Sarah and John.
OK finally found it as Ann rather than Anne. Goverrnement website search engines are really good arent they Age 78 so DoB 1752.
Glad you managed to find it (I often have to change it from "Exact Matches Only" to "Similar Sounding Variations" to find the record I want). I think an age at death of 78 in 1840 actually implies a birth around 1762 rather than 1752.
Given the revised birth year of 1762, I think this baptism of Ann Waghorn, daughter of William and Mary, on 21 July 1762 at St Mary's, Lewisham looks quite promising - https://www.freereg.org.uk/search_records/5d866fe4f493fdd4f29e2acb.
It looks like she also married James at St Mary's, Lewisham in 1779 - https://www.freereg.org.uk/search_records/5ae5835af493fd14df01232b.
There is another issue with this family. The William Waghorn who was married to Mary Ray left a Will. That Will was signed by him on 29 June 1774, so he can't have died in 1771. The Will is available for free from the National Archives at PROB/1002/124.