Jamie Lynn Spears: I Had to 'Separate Myself from My Family' but I 'Love and Support' Britney

Jamie Lynn Spears is opening up about her complicated family dynamic.

Ahead of the Jan. 18 release of her memoir Things I Should Have Said, the actress and country singer-songwriter, 30, addresses her relationship with her older sister Britney in the new issue of PEOPLE.

Since June — when Britney, 40, first spoke out in court against her long-held conservatorship, which was terminated by a judge in November after 13 years — fans of the superstar have attacked Jamie Lynn online, accusing her of not supporting Britney during the conservatorship; she's even gotten death threats. Last week, Britney unfollowed Jamie Lynn on Instagram. (Jamie Lynn still follows her sister.)

"I've only ever tried to be helpful, so any notion that says the contrary is just completely ridiculous," Jamie Lynn, 30, says of her strained relationship with her sister, 40, who has repeatedly criticized her family on social media over the last six months.

For Jamie Lynn, "it was really important for me to separate myself from my family to focus on the family I've created, which is me, my husband and my daughters. Setting those boundaries in place was really important," says the Sweet Magnolias actress, who is raising daughters Maddie, 13, and Ivey, 3, with husband Jamie Watson, 40. "I am not my family. I am my own person. I fought very hard and worked very hard to establish myself and to build the life that I have today."

After years of trying to keep up appearances, Jamie Lynn is now quick to admit "no family is perfect."

In 2008, the same year Jamie Lynn welcomed Maddie at age 17, Britney was placed under a conservatorship following a public breakdown, and their dad Jamie and others made all of her personal and financial decisions until its termination last November. (Britney's diagnosis and medical records remain private.)

"I didn't have a say when [the conservatorship] happened. My sister was going through a hard time, I was still a child, and that's what everybody, I think, forgets: I was just a kid going through my own crap," says Jamie Lynn, who adds Britney was like a second mother to her growing up. "I was still a cheerleader, and I remember I'd go to games and people would say stuff. I was so angry and sad and worried. I knew things weren't OK, but you don't know how to put that in words as a kid."

As an adult, "I was asked to be a part of [the conservatorship], and I took time, and I declined it nicely," says Jamie Lynn, who, according to court documents, was appointed as trustee of Britney's multimillion-dollar estate in 2018 but never filled the role. "I just wanted to remain her sister, very simply. It's unfortunate that I've been grouped into this, but the facts are I had nothing to do with anything."

For now, the Spears family remains fragmented after Britney accused her dad of conservatorship abuse and claimed her family "never showed up" for her amid the saga. (Jamie, mom Lynne and Jamie Lynn have all denied wrongdoing.)

"I love and I support my sister, and I always will. It's very clear that this has been a painful process, and I have to respect however she works through that. This is a complicated situation," says Jamie Lynn. "It gets to a certain point where you can't help someone who doesn't want you to. If it starts to become harmful or unhealthy for you and your well-being, then you have to remove yourself. My intentions have always been pure when it comes to my family."

Today, Jamie Lynn adds, "My biggest regret is that I should have just said all this s--- a long time ago. We would've saved ourselves a lot of headaches, I think."

For more on Jamie Lynn Spears — including an exclusive excerpt from her book, Things I Should Have Said — pick up the new issue of PEOPLE, on newsstands everywhere Friday.