Hi bannatyne,
Did you mean your g-grandmother was called Agnes?
If so there is an Agnes Andrew on the 1841 Census at Port Patrick age 2
Morecroft Port Patrick
Shusan Wither age 35 Farmers wife
Helean Wither age 11 Daughter
Margret Wither age 2 Daughter
Janet Hayslop age 25 Lodger
Agnes Andrew age 2 Daughter of J Hayslop
John Cleary age 10 Son of J Hayslop
Helen Swetn age 3 Daughter of J Hayslop
All born Wigtownshire.
These spellings and descriptions are as transcribed on
www.freecen.org.uk.
Could this be the child you mention in your post with mother and siblings?
Looby