Mattie, a devout Catholic, lived by the philosophy expressed in Psalm 118, "This is the day the Lord is made. Let us rejoice and be glad."

She was born April 1st, 1937 to Leo and Adeline Schirber in Mobridge, South Dakota, the youngest of five children. Mattie met the love of her life, Bob Sieler, at the age of five in kindergarten which extended to a 64 year marriage. She graduated from Mobridge High School and went on to the St. Catherine's University in Saint Paul, MN and ultimately graduated from the University of South Dakota. Bob and Mattie were married in 1959 and then moved to Wall, SD to begin their teaching careers. In 1964, they moved to Las Vegas, NV where Mattie served as a high school librarian. During summers, the family looked forward to retreats at Cabin Minnelusa in the Black Hills of South Dakota.

Survivors include her husband, Robert Sieler, daughter Dr. Pamela Runfola, son-in-law Dr. Mark Runfola, grandson Anthony Runfola, sister Virginia Miller, sister-in-law Cathy Schirber, brother-in-law Felix Tristani, and sister-in-law Anne Sieler, and numerous nieces and nephews.

She was preceded in death by her parents Leo and Adeline Schirber, brother James Schirber, and sisters Bibiana Tristani, and Mary Jo Marshall.

In lieu of flowers, memorials can be made in Mattie's name to St. Vincent de Paul Charity or Stillwater Hospice.