I don't have an obituary, but her record in the IL Death Record lists her parents as William C. Brooks and Sarah Marie Roberts:
Anna Brooke Mason, "Illinois Deaths and Stillbirths, 1916-1947"
Name: Anna Brooke Mason Titles and Terms (Original): Event Date: 12 Jan 1926 Event Place: Williamsville, Sangamon, Illinois Gender: Female Marital Status: Race: Age: 83 Birth Year (Estimated): 1843 Birth Date: 03 May 1842 Birthplace: Deleware Father's Name: William Co...Ay Brooke Father's Titles and Terms: Father's Birthplace: Maryland Mother's Name: Sarah Maria Roberts Mother's Titles and Terms: Mother's Birthplace: Deleware Occupation: None Residence Place: Address: Spouse's Name: Spouse's Titles and Terms (Original): Spouse's Birthplace: Burial Date: 14 Jan 1926 Burial Place: Cemetery: Auburn Cem. Informant's Name: Additional Relatives: Digital Folder Number: 4008164 Image Number: 2221 GS Film number: 1613169 Reference ID: 3071
Citing this Record
"Illinois Deaths and Stillbirths, 1916-1947," index, FamilySearch (https://familysearch.org/pal:/MM9.1.1/NQH3-VLW : accessed 07 Nov 2013), Anna Brooke Mason, 12 Jan 1926.
You can find Anna with her family in Sangamon County in the 1860 census, father listed as W.C. Brooks, mother Sarah, Anna as A.V. Her father is not listed in the 1870 census, but her mother is still there along with younger children, Amy and Horace. Anna is listed with her husband George Mason in the 1870 census.
This family can also be found in the 1850 census in Port Penn, New Castle, Delaware.
Online sources show that Sarah M Roberts married William C. Brooks June 19, 1825 in Delaware.
The 1880 census of Sangamon County shows Horace M Brooks, the youngest child listed in the 1870 census living with William P. Brooks and family. William P's record in the IL Death Index shows that he is an older sibling of Anna, with his parents listed as William Conway Brooks and mother as Sarah Marish Roberts (could be a typo). In 1880 Horace is listed as a nephew, suggesting that his father was a brother of William's and that in 1870 Horace was living with his grandmother.
You might try contacting the Springfield Public Library to see what they would charge to search for/copy an obituary, since you have the exact date of her death to see what additional information is mentioned. She apparently had several siblings who lived in Sangamon County.