It looks like Isabella's parents were Philip Shimmin and Isabella Gelling who md 9 Jun 1827 Braddan
There are christenings for all the children except Isabella. However, she was with them in the 1851 Census in Ballaugh parish.

1851
, Ballaugh, 02-30, 002, SHIMMIN, Phillip, Corvalley, Head, Married, 49, Farm 60 Ac, Douglas
, Ballaugh, 02-30, 002, SHIMMIN, Isabella, Corvalley, Wife, Married, 45, Farmers Wife, Douglas
, Ballaugh, 02-30, 002, SHIMMIN, Robert, Corvalley, Son, Unmarried, 18, Farmers Son, Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, Isabella, Corvalley, Daughter, Unmarried, 16, Farmers Dau, Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, Margaret, Corvalley, Daughter, , 14, Scholar, Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, William, Corvalley, Son, , 12, Scholar, Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, Jane, Corvalley, Daughter, , 10, Scholar, Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, Thomas, Corvalley, Son, , 9, Scholar, Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, James, Corvalley, Son, , 7, Scholar, Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, Eleanor, Corvalley, Daughter, , 4, , Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, Edward, Corvalley, Son, , 2, , Ballaugh
, Ballaugh, 02-30, 002, SHIMMIN, Sarah R., Corvalley, Daughter, , 4mos, , Ballaugh

Thomas Curry Lace was ch 8 Jul 1834 Maughold parish s/o Daniel Lace and Frances Elliott who md 30 Jun 1832 Saint Andrew, Newcastle Upon Tyne, Northumberland, England
I didn't see any other children for the couple and didn't find them in the 1851 census.

Chances are Thomas and Isabella were md in Ballaugh though I didn't see an entry in the IGI for the marriage.

Ballaugh Monumental Inscriptions
Old Yard
Q 1
In loving memory of Phillip Shimmin of Corvalley, Ballaugh who died April 28th 1894 aged 92 years
Superintendent of the Parochial Sunday School for over 50 years
He died as he lived happy

Q2
In memory of Isabella wife of Philip Shimmin of Ballaugh sho died September 28th 1878 aged 73 years

Q3
In memory of Thomas son of Philip & Isabella Shimmin of this Parish who died June 29th 1851 aged 9 years

Q4
Sacred to the memory of Rachel Corlett alias Shimmin wife of John Corlett of Ballakinnag who departed this life the 2nd of November 1849 aged 20 years
I shall go to her but she shall not return to me

Q5
In memory of James son of Philip & Isabella Shimmin of this Parish who died June 27th 1871 aged 27 years