Her father mentions Mary in his Will. However, there is no mention of Mary, only a Margaret, in a blue hand-written document of unknown source collected by Brian Oliver of nzolivers.com (b.1950) on his April 2008 visit to Devon. Could this be the same person?

Year of birth is from the blue hand-written document of unknown source.

Brian of nzolivers has since concluded that their were two separate Oliver familys in Devon at the time, headed by a John and Grace. Margaret was part of the other Oliver family based in Ashwater and in Halwell.

Name of Mary, date and place of baptism, from records online for Parish of St Giles on the Heath in the County of Devon, as alerted by Katia and Tim Oliver In an email dated 4 January 2021.
Tim Oliver is a x3 great grandson of James and Ruth Oliver, his grandfather being Ivor James Clark Oliver (1907-1989).
Name: Mary Oliver
Event Type: Baptism
Event Date: 02 May 1813
Event Place: Parish of St Giles on the Heath in the County of Devon, England
Father's Name: John Oliver
Parent's Abode: Tetcott, Devon
Father's Trade or Profession: Yeoman
Mother's Name: Grace Oliver
From Scans of original parish registers from Cornwall [including Devonshire] containing baptisms from 1538 to 1910 published on FamilySearch:
https://familysearch.org/ark:/61903/1:1:QGLK-PP1H
Note: Login to FamilySearch required

Date and place of Marriage, from Devon Marriages and Banns records received from Katia, wife of Tim Grant Oliver, in the email dated 19 December 2022:
First name(s): Mary
Last name: Oliver
Marriage year: 1837
Marriage date: 21 Jun 1837
Spouse's first name(s): Henry
Spouse's last name: Goodman
Place: North Petherwin
Parish: North Petherwin
Denomination: Anglican
County: Devon
Country: England

Katia, wife of Tim Grant Oliver, in the email dated 19 December 2022 writes, "The Will [of father William Oliver] looks like it says that Ann was in England and Mary was in the USA. Henry and Mary's daughter's name Jane Lean "Jennie" Rea matches with the will. Jennie was born in Ohio".

Name of other children, estimated year of birth, estimated emigrated to USA between 1844 and 1846, from the 1860 Federal Census of Free Inhabitants in Independence Township, Washington County, Ohio USA enumerated on 6th day of August 1860, found in February 2023:
Henry Goodman, 56, Male, Farmer, Real Estate value $1,000, Personal Effect value $300, Born England, [Born circa 1804]
Mary Goodman, 49, Female, Born England [Born circa 1811]
John H Goodman, 16, Born England, [Born circa 1844]
Sarah J Goodman, 14, Born Ohio, [Born circa 1846],
William Goodman, 12, Born Ohio, [Born circa 1848],
Jane L Goodman, 9 Born Ohio [Born circa 1851]
Elizabeth Goodman, 6, Born Ohio, [Born circa 1854]

From the above Census, son John was born in circa 1844 in England, and daughter Sarah born in Ohio. Therefore, emigrated to the U.S. circa 1845.
As of February 2023, no record of sailing to America could be found. At one stage Brian of nzolivers thought they may have travelled on the Ship Royal Adalaide but dates/ages (arriving New York 21 Apr 1840) do not match.

Date and place of death, estimated date of birth, from a link to the Records of Deaths Probate Court received from Katia, wife of Tim Grant Oliver, in an email dated 7 February 2023:
Name: Mary Goodman
Date of Death: 25 June 1892
Condition: Widowed
Age: 82 years 1 month
Place of Death: Independence Township, Washington, Ohio
Place of Birth: England
Occupation: Housekeeper
Color: White
Cause of Death: Paralysis [Complete or partial loss of muscle function - sometimes due to stroke or injury]
Place of Residence: Independence Township, Washington, Ohio

NOTE: From the above age of 82 years 1 month, this would place Mary’s birth at 25th May 1810. However, brother William was born 3rd August 1810. So, this does not work. Was Mary in her 82nd year and born in 1811? This latter year matches the 1860 Census above. At this stage I will use “circa May 1811” as date of birth.