Phillip Faraone/FilmMagic; Michael Loccisano/Getty Images Britney Spears and Jamie Lynn Spears
The Sweet Magnolias actress, 30, posted an Instagram Story Friday that reads, "Nobody trashes your name more than someone who's afraid you'll tell people the truth."
Just hours before, Britney, 40, accused Jamie Lynn of spreading "crazy lies" after Jamie Lynn alleged during her recent interview with Nightline that Britney once pulled out a knife and locked the two of them in a room.
"Jamie Lynn... congrats babe! You've stooped to a whole new level of LOW... I've never been around you ever with a knife or would I ever even think to do such!!!" Britney wrote in part, adding, "The only knife I ever saw you with at home was cutting the biggest pieces of squash I ever saw in my life and it was way too big for me to cut... So please please stop with these crazy lies for the Hollywood books!!! NOW and only NOW do I know only a scum person would make up such things about someone...."
Jamie Lynn Spears/instagram
Jamie Lynn previously told Nightline's Juju Chang that Britney has often exhibited "erratic, paranoid and spiraling" behavior, recounting a time when her older sister once became "scared," took out a knife and locked the two of them in a room.
The sisters' feud sparked after Jamie Lynn appeared on Good Morning America Wednesday to discuss her new memoir, Things I Should Have Said, out Jan. 18. While there, she opened up about her relationship with Britney and the end of the "Gimme More" singer's conservatorship, which was terminated in November. Jamie Lynn explained that when the conservatorship was put into place in 2008, she was pregnant with her first child at 17 years old and focused more on becoming a mom and less on her sister's legal situation.
Britney responded in a lengthy post Thursday, sharing what "bothered" her about Jamie Lynn's remarks.
"She was never around me much 15 years ago at that time .... so why are they even talking about that unless she wants to sell a book at my expense??? REALLY???" Britney wrote. "Then where the lady mentioned why did she accuse you of doing remixes to her songs ... I know it may sound like a silly thing to most people but I wrote a lot of my songs and my sister was the baby. She never had to work for anything."
RELATED VIDEO: Jamie Lynn Spears Says She Has Nothing 'But Love & Support' for Sister Britney in New Interview
Fans of the superstar have attacked Jamie Lynn online, accusing her of not supporting Britney during the conservatorship. She's even gotten death threats.
Jamie Lynn shared in this week's issue of PEOPLE, "I've only ever tried to be helpful, so any notion that says the contrary is just completely ridiculous."