Nashville shooting victim and school headmaster Katherine Koonce was a 'mighty oak tree of a woman' who advocated for students with disabilities, a longtime friend says

Katherine Koonce (left) and a vigil at The Covenant School (right)

The Covenant School // John Amis/ AP

• Katherine Koonce was one of six who died in the mass shooting at Nashville's Covenant School Monday.
• Anna Caudill, Koonce's friend of 23 years, spoke to Insider about the school headmaster's legacy.
• Koonce was a 'mighty oak tree of a woman,' Caudill told Insider. 

Katherine Koonce spent so much time advocating for the lives of her students — all while raising two children of her own ...