Hi
This baptism is on the IGI:
Dorothy Armstrong b.7/9/1818, bp.27/8/1819 Redwing Congregational Chapel, Alston, Cumberland, d. of William (no wife shown)
also a sister baptised same time
Mary Armstrong b.16/4/1816, bp.27/8/1819 ditto
There are a number of Armstrong baptisms there - some to a William and Dorothy and some to William and Mary.
However, in 1822 there are another 2 baptised together - John b.1820 and William b.1822 on 30/9/1922 and these are to William and Dorothy. I would think with this pattern and Dorothy's christian name that parents were William and Dorothy.
Annette