Mrs Leonard, 51, died at the scene but Conor was taken to hospital where he received stitches for stab wounds.
The injured son of murder victim Concepta Leonard has been praised for his courage in the moments after he and his mother were stabbed at their home.
Her son Conor, who has Down's syndrome, summoned help by via an alert system that had been installed in their home, according to their family priest.
"On Monday afternoon in the light of a May-day evil intent visited this peaceful community".
"We see him holding her hand to reassure her and we see him finding the courage and confidence to seek help". Why should such a awful thing happen to such a lovely person?
"Where is our God in this moment of evil?. Circumstances could have been different". "Because for her, she had Conor with her, and that was the most important person she wanted with her at that moment".
Mourners at the funeral of Concepta "Connie" Leonard, who was brutally killed by her estranged partner in a murder-suicide, have been told the horrific circumstances of her death can't "destroy the love in her heart and soul". "So today we celebrate all that was loving, tender and handsome in Connie's life", Fr Gallagher said.
"She possessed so many handsome gifts, but she carried them in a very unassuming, humble way".
Ms Leonard was born into a family home filled with the sound of music and from the age of six she travelled with her father Dinnie to music sessions and fleadhs all over Ireland, winning three all-Ireland medals in accordion and piano, mourners heard. All over the county and beyond.
"With her energy and enthusiasm, her infectious smile and the twinkle in her eye, she has left a legacy of musical talent for generations to come".
Fr Gallagher also told the congregation how her son, Conor, was at the heart of everything for Connie.
He also paid tribute to Conor in his homily preached at St Mary's Church in Brookeborough and said he was at the "heart of everything in her life" and "together they developed friendships and lived experiences that most of us could only dream about". But in some way the absence of a mother's love was reclaimed when she gave life to her own son Conor.
"She was a devoted mother and together they shared a special bond of love. His love and his affection will be a source of healing for all, he is the light that will renew the spirit of hope in our lives", Fr Gallagher added.
Police are treating the attack on Conor Leonard as attempted murder.