"None of us wanted her to marry him," she said as she held back tears. "We did not like how he treated her."
She was on the stand for about 50 minutes. Hudson's sister, Julia, later told the jury her ex-husband allegedly made numerous death threats against her family saying, "If you leave me, you will be the last to die. I'll kill your family first."
Balfour showed little emotion during opening statements and Hudson's testimony. He has pleaded not guilty to three counts of first-degree murder in the October 2008 slayings of Hudson's mother, brother and 7-year-old nephew.
Prosecutors say Balfour was in a jealous rage because Hudson's sister was dating another man.
Hudson has vowed to be in the courtroom every day of the trail. Legal experts say the jury will be watching her every move because of her celebrity.
"If it is genuine pain that she expresses, it will help the prosecution," said Ron Safer, a legal expert. "If the jurors feel that she is over reacting or acting in any way, it will hurt."
If convicted, Balfour faces a mandatory life sentence.
The Associated Press contributed to this report.