Only a week before, Diaz celebrated her 25th birthday.
"She was a great mom, loved her kids," said McGowan. "I have kids and she, all of our kids were each other's kids, you know, she was always about the kids."
According to Floyd County Sheriff's Office, Diaz was found Saturday in the home of 50 year old Edward Hernandez, who was her boyfriend. Hernandez had called police himself to tell them about the murder.
He's been arrested for the murder and is currently in Hale County Jail on $500,000 bond.
"When I find out my sister's been murdered by this son of a b***h who says he loved her then, you know, I couldn't believe it," said McGowan. "My first reaction was this is all a lie, its a nightmare I can wake up from but it hasn't happened."
McGowan says Diaz wanted to leave her boyfriend, Hernandez, to spend more time with her children.
"They argued and fought all the time but never once did we hear about him laying a hand on her," said McGowan. "She told him that she didnt want to be with him anymore, that she was leaving him to go back with Rowland, which is her husband to be with her kids and he told her if he couldn't have her then nobody could."
McGowan hopes by speaking about her sister's death, she can keep another family from feeling this kind of pain."I don't want this to be somebody else's family going through what we are," said McGowan.