Jamie Lynn Spears describes alleged incident where sister Britney 'got in her face' with her daughters present

Jamie Lynn is promoting the upcoming release of her memoir, 'Things I Should Have Said'

Jamie Lynn Spears is opening up about two emotional incidents involving her sister, Britney Spears.

Jamie Lynn, 30, is promoting her upcoming memoir, "Things I Should Have Said." The book covers her family, career, and what it was really like to grow up in the shadow of her sister, one of the world's biggest pop stars.

In an interview that aired on "Nightline" on Wednesday, the mother of two discussed two incidents she penned in her memoir. The first allegedly involved Britney becoming "really angry" with Jamie Lynn while she was holding her toddler, Ivey. 

"She cursed at me and so I walked out of the rooms. I was like, we're just all family under one roof. I'm not trying to argue. And when I try to remove myself from the situation, that's when I guess she just got really angry and my oldest daughter tried to, you know, mediate the situation," Jamie Lynn recalled.

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Britney Spears and Jamie Lynn Spears   (Photo by KMazur/WireImage)

Britney Spears and Jamie Lynn Spears   (Photo by KMazur/WireImage) (KMazur/WireImage)

"I hated that, like, that's not what you're supposed to do, you're 12," Jamie Lynn added of her oldest daughter, Maddie.

At the time, Jamie Lynn said her parents informed her she "shouldn't be upset" and that she "can't upset Britney."

"I said you just saw me and my children be upset. When will I matter?" Britney's little sister added.

Jamie Lynn also described to ABC's Juju Chang an incident that occurred when she was "a kid" and Britney said she was scared and took a knife and locked them in a room.

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Britney Spears and her sister Jamie Lynn Spears at The Teen Choice Awards, held at the Universal Amphitheatre in Los Angeles, California, August 4, 2002.

Britney Spears and her sister Jamie Lynn Spears at The Teen Choice Awards, held at the Universal Amphitheatre in Los Angeles, California, August 4, 2002. ( Kevin Winter/Getty Images)

"First off, I think that experiencing my own panic attacks and how sometimes we can feel in those moments is important," Jamie Lynn said of her decision to include this memory in her memoir. 

"But also it's important to remember that I was a kid in that moment. I was scared. That was an experience I had. But I also was fearful to, like, really say anything because I didn't want to upset anybody or anything. But I also was so upset that she didn't feel safe," she continued.

The 30-year-old younger sister of Britney Spears broke her silence on Wednesday about her current rift with the pop star. In a tearful interview, Jamie Lynn revealed she "100%" loves her sister and denied playing a role in her conservatorship, which was dissolved in November.

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In part two of an interview that aired Wednesday on "Good Morning America," the former "Zoey 101" star said there was a time she too faced isolation. At 16, Jamie Lynn became pregnant with her first child, causing photographers to follow her movements. She writes in her book, "The entire Spears team was already caught up in my sister's PR difficulties and everyone around me just wanted to make the issue disappear."

Jamie Lynn and Britney Spears.

Jamie Lynn and Britney Spears. (Image Group LA/Disney Channel via Getty Images)

Jamie Lynn was sent to a remote cabin to avoid the news, the interview revealed. She had no cell phone and no contact with the outside world.

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"It felt like you're almost suffocating. It was just like, I felt like, what was I going to do? I was a kid and maybe this is in my best interests and maybe this is what I'm supposed to do because of course I don't want to be hounded by the paparazzi or tabloids or allow them to control my narrative. But it felt like I was really being alienated," Jamie Lynn said.

Jamie Lynn gave birth to her and then-boyfriend Casey Aldridge's first child, daughter Maddie, in 2008. She also shares daughter Ivey, 3, with her husband, Jamie Watson.