The 'Real Housewives of Beverly Hills' star - who has kids Mason, eight, and Jake, five, with ex-husband Eddie Cibrian - admits she flew into a jealous rage when she saw the 29-year-old singer with her former spouse and her young sons for the first time.
She told Australia's NW magazine: ''I remember walking up to soccer practice and there she was with my baby in her lap.
''My blood was boiling, and I thought I was going to kill her. I really thought I was going to physically hurt her.
''That was the first time I saw her that way - she was sitting in my soccer chair, under my tent, she's got my kid on her lap and she's with my husband, and that was that little moment of total irrational fury.''
Despite her comments, Brandi - who split from Eddie in 2009 after almost 10 years of marriage after he began an affair with LeAnn on the set of 'Northern Lights' - insists relations with the 'How Do I Live?' hitmaker are now better and she is pleased the singer gets on well with her children.
She added: ''We're never going to be best friends, but she's good to my kids, they love her and that's all I could ask for.
''If they didn't like her, I'd be in court right now, fighting. It's not about me - it's about them.''
Last month, Eddie and LeAnn renewed their wedding vows on the first anniversary of their marriage.