You basically have to win the league or tie for the title. There have only been 3 instances in 22 years where the COY didn't finish 1st/T-1st. 2016 and 2017 appear to be the "because Kim has gotten it 4 of the last 5 years" clause.
1997 Marian Washington, Kansas (1st)
1998 Marsha Sharp, Texas Tech (1st)
1999 Marsha Sharp, Texas Tech (1st)
2000 Sherri Coale, Oklahoma (T-1st with ISU and Tech; ISU was #1 seed)
2001 Sherri Coale, Oklahoma (1st)
2002 Deb Patterson, Kansas State (T-3rd; went from 2-14 to 11-5)
2003 Jody Conradt, Texas (1st)
2004 Jody Conradt, Texas (T-1st with KSU)
2005 Kim Mulkey, Baylor (1st)
2006 Sherri Coale, Oklahoma (1st)
2007 Gary Blair, Texas A&M (T-1st with OU)
2008 Deb Patterson, Kansas State (1st)
2009 Sherri Coale, Oklahoma (1st)
2010 Connie Yori, Nebraska (1st)
2011 Kim Mulkey, Baylor (1st)
2012 Kim Mulkey, Baylor (1st)
2013 Kim Mulkey, Baylor (1st)
2014 Mike Carey, West Virginia (T-1st with BU)
2015 Kim Mulkey, Baylor (1st)
2016 Jim Littell, Oklahoma State (T-4th)
2017 Karen Aston, Texas (2nd)
2018 Kim Mulkey, Baylor (1st)