As suggested, I've searched for other offspring from the marriage of William WILLS and Mary

?, but with no luck. I've also searched for their marriage and found 3 (very distant) possibilities:-
1. 1 Dec 1705 Wm WILLS to Mary CHAPEL in Lanteglos-by-Camelford (34m to Mylor)
2. 25 Feb 1706 Wm WILLS to Mary HOOPER in Bradoc (28m to Mylor)
3. ??

1700 Mr Wm WILLS to Mrs Mary R??? in St Ives (20m to Mylor)
I've used Family Search, Cornwall OPC, FindMyPast and FreeReg
Any of these could be Jane's parents.
Concerning the absence of any further WILLS offspring, there are burial record for Mary WILLS:-
1. 29 Jan 1706 in Braddock
2. 01 Dec 1710 in Lanteglos-by-Camelford
3. 09 Nov 1715 in Lanteglos-by-Camelford
4. 06 Dec 1716 in St Gluvias (dr of Mr John & Mrs Mary)
This last was , presumably, an infant, so definitely not the mother of Jane.
The Braddock burial took place a month
before the marriage of Mary HOOPER, so cannot refer to her. Probably, one of the Lanteglos burials is that of Mary nee CHAPEL, which, if she was Jane's mother, would explain the absence of further offspring.
All very interesting, but is my research any further advanced?