Bonnie McKee Reveals Which of the No. 1 Hits She Co-Wrote for Katy Perry Are Most Meaningful to Her (Exclusive)

McKee tells PEOPLE writing with Perry "was a really unexpected turn in my career that changed my life"

• After a serendipitous run-in with Katy Perry, Bonnie McKee went on to co-write five No. 1 hits with the superstar

• McKee, whose new album Hot City is out now is reflecting on their work together — and revealing her favorite tracks

• As Perry works on her next album, McKee says she's "so excited to hear the new stuff that's going to come"
  

Bonnie McKee could have never predicted one trip to a vintage store would lead to having several No. 1 hits under her belt.

The singer-songwriter, whose new album Hot City is out now, was fresh off getting dropped from her first recording contract when she went to sell her clothes at Wasteland in Los Angeles — and met Katy Perry, with whom she'd go on to write five chart-topping songs.

"We met in line, and she was a fan of my first album," McKee tells PEOPLE, referring to 2004's Trouble. "We were fast friends, and then she ended up bringing me in on [her] second album, Teenage Dream."

After attempting to launch her own career as an artist with Trouble, the "American Girl" musician had found herself down on her luck and turned to songwriting, crafting lyrics for stars like Elliott Yamin, Leighton Meester and Kelly Clarkson. But working with Perry and hitmakers Lukasz "Dr. Luke" Gottwald, Max Martin and Benny Blanco took McKee to the next level.

Together, she and Perry co-wrote "Teenage Dream," "Last Friday Night," "California Gurls," "Part of Me" and "Wide Awake" from the Teenage Dream era — all of which reached No. 1 on the Billboard Hot 100. Following the success, they linked back up to write the No. 1 hit "Roar" as well as "Birthday" and "Legendary Lovers" for Perry's 2013 Prism album.

"I suddenly went from being completely broke, not having a car, my cell phone turned off, not having hot water and digging for Taco Bell money to house-hunting in Hollywood Hills," recalls McKee. "It was really surreal."

Around the same time, she also co-wrote the Hot 100 chart-topper "Hold It Against Me" for Britney Spears and other global hits including Taio Cruz's "Dynamite," Rita Ora's "How We Do (Party)" and Cheryl's "I Don't Care."

Looking back, McKee knows which No. 1 hits are her favorites: "It's a tie between 'Teenage Dream' and 'Roar.'"

Before crafting the track, the Grammy-nominated songwriter came up with the title of "Teenage Dream" and initially wanted to keep it for herself, as she was looking to get back into releasing her own music.

"It was kind of my 8 Mile moment, where I had to look in the mirror and be like, 'You only get one shot.' I was like, 'OK, I have a great idea, and I need to share this because I think it's going to take this on to the next level. I'm going to be a team player,'" McKee explains, "and then Katy and I wrote the rest together."

"Roar," on the other hand, was born out of a bonding session between McKee and Perry. "It's a feminist anthem, but it's also just a song for anyone who feels oppressed or not empowered in whatever situation they may be in," says the songwriter.

"The feedback that I've gotten about that song — people telling me help them get through the divorce, that it helped them be inspired to get in shape or it helped them through their battle in cancer, or whatever kind of heavy stuff — was incredibly powerful to hear, that it could have an impact on people like that," adds McKee. "So, for creative reasons I love 'Teenage Dream,' and for spiritual reasons I love 'Roar.'"

Given McKee's ambitions of writing and releasing music for herself at the time, she admittedly felt a little jealousy "in the beginning," as she watched her lyrics reach the top of the charts, but sung by Perry. However, such feelings faded as she realized the impact their work had on culture.

"Because I wasn't where Katy was at yet in my own career, I was like, 'This actually has a chance to live and to reach people.' And ultimately, that's what I want to do — reach and touch the most people that I can with my art," she says. "So I went very quickly from feeling kind of jealous to being like, 'This is amazing, and I'm just so grateful to be here. I'm so lucky to be a part of this,' because it ended up being a part pop culture history, and I couldn't have done that on my own."

McKee's since continued songwriting for other artists, including Bebe Rexha and Ava Max, but she's also gotten back to focusing on her own work with Hot City, her first full-length solo album since Trouble.

Perry, meanwhile, has been teasing her next era. Would McKee consider getting the powerhouse "Teenage Dream" duo back together to write more hits?

"I haven't gotten a call. If I got the call, I would answer, but it's also not something for me to invite myself to," she says. "Also, I think Katy and I have proven we're great together, and there's so many other incredible up-and-coming songwriters that also deserve to have a spot on a Katy Perry album."

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McKee predicts the timing for her and Perry to write together ultimately may not have worked out, as she's been spending time working on Hot City while the "Never Really Over" singer makes her next album.

"I feel like Katy and I are kind of synced in that way. It's like, whenever she's putting something out, I'm also cooking something. It's really hard to do both at the same time, but I love Katy," she says. "I'm so excited to hear the new stuff that's going to come because I know some of the people that are working on it, and I think it's going to be great."

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