LeAnn Rimes Calls Song She Wrote for Husband Eddie Cibrian 'Magical': 'I Didn't Know If I'd Ever Share'

When LeAnn Rimes married actor Eddie Cibrian in 2011, she knew she wouldn't be able to sing to him at their wedding. Instead, she wrote him a song as a gift for their special day.

"how much a heart can hold," written by Rimes, Darrell Brown and David Baerwald, is her love letter to the life she shares with Cibrian.

"It was one of those songs I didn't know if I'd ever share," Rimes tells PEOPLE, explaining it's so personal that she still cries sometimes when she sings it. "But we put it on a video for our anniversary last year on Instagram, and people were like, 'What is this song?'"

Rimes chose to release the song now because she believes "how much a heart can hold" fits the story of her new album god's work, which will be in stores Sept 16. The tender and profoundly personal ballad is immediately available to those who preorder the album now.

"People just loved it when I shared it last year, and I was like, 'OK, I feel like this is song should be out there," she says. "I'm known for my love songs, I think. And it just felt like maybe people need to use it at their wedding, too. I love it. It's a magical song."

Rimes also sang "how much a heart can hold" on CMT Crossroads: LeAnn Rimes & Friends, premiering at 8 p.m. ET Thursday on CMT. Other artists on the show include Carly Pearce, Mickey Guyton, Ashley McBryde and Brandy Clark, who collaborate on Rimes' extensive list of popular songs.

Throughout her 25-year music career, Rimes stacked up hits including "Blue," "How Do I Live," "One Way Ticket," "I Need You" and "Probably Wouldn't Be This Way." She is an international, multi-platinum-selling singer/songwriter. She has sold more than 48 million units and, at 14 years old, became the youngest solo artist to win the prestigious best new artist at the Grammy Awards. "How Do I Live" holds the record as Billboard's Hot 100 all-time No. 1 hit by a female artist.

But more than that, McBryde says, she treasured Rimes' music for the way it brought her family together.

"'Blue' and 'One Way Ticket' were a big deal in my household," McBryde tells PEOPLE. "Even my father learned to play 'One Way Ticket.' And when 'Nothing Better to Do' came out, I was like, 'That's it. That's sass.'"

McBryde, 38, says the attitude in the song perfectly fit her personality and made her feel like country music was her home.

"Now, here we are all these years later, and I'm standing on the same stage as her," McBryde marvels.

Brandy Clark says the most important thing about their time spent filming CMT Crossroads: LeAnn Rimes & Friends was to "lift LeAnn up."

"Her music has meant so much to so many of us," Clark, 46, says. "I think she's one of the greatest country singers ever. Both she and Wynonna are often not talked about enough when we talk about world-class vocalists in this format. It breaks my heart that she feels like no one remembers her. I hope she was able to receive the four of us reminding her that she's a big deal."

CMT Crossroads: LeAnn Rimes & Friends is part of Rimes honoring her 25th year in music. She released "Blue" when she was 13 years old. She's now 39.

"It is overwhelming [to think about]," Rimes says of her storied music career. "It seems like most of my life has been spent in music, and it's hard to fathom a world outside of it. I feel so grounded in this has just been such a part of my being in this lifetime. I'm just proud to have left the work that I have, and I'm proud to only be 40. I have the rest of my life ahead of me to do what I love."