Wilson, 34, was a singer-songwriter and the father of McCready's infant son. He was found dead of an apparent self-inflicted gunshot wound Jan. 13 and his death remains under investigation.
Asked in a soon-to-air "Dateline" interview if she shot Wilson, McCready replied: "Oh, my God, no. Oh, my God, no. ... He was my life. We were each other's life."
Pressed to disclose whether she believed "100 percent" Wilson committed suicide or whether he might have been murdered, the singer grew quiet, then said, "I don't know."
McCready also denied rumors claiming Wilson had cheated on her shortly before he died.
"David was not having an affair with another woman. That is absolutely totally untrue," McCready said.
"I've never gone through anything this painful, nor will I ever again go through anything as painful," she added.
The "Dateline" interview was excerpted on Tuesday's edition of the "Today" show.
E! News said Wilson's friends are baffled by why the new father would want to kill himself. They also said McCready did not attend a Jan. 19 memorial they arranged for him.
McCready's once-bright career has been sidelined in recent years by her battles with substance abuse, suicide attempts and legal woes.