She is listed as Maude C. Riley and they do not have a deathdate for her. Charles, her husband, died 21 January 1923, and the Deaths and Stillbirths index at Ancestry says that his wife was Maud and that he was buried at Oak Ridge Cemetery in Springfield.
I cannot find Carrie or Maude Riley listed in the Deaths and Stillbirths index at Ancestry, and I did not find her in the 1940 census or the IL death index from the Sec of State's office. I wonder if you contacted the Oak Ridge Cemetery office if they could give you her date of death.
Their contact information is: Springfield City - Office of Public Works, Oak Ridge Cemetery 1441 Monument Avenue Springfield, IL 62702 Phone: 217-789-2340
There are some 53,000 burials in this cemetery, so I'm assuming they have and index.