In January 2018, she appeared in a Christina Aguilera-themed episode on Lip Sync Battle competing against Taye Diggs. She performed Aguilera's famous hits "Fighter" and "Genie In a Bottle". She has also previously performed at Aguilera's 36th birthday party in December 2016. On March 5, 2018, she appeared as a guest co-host on FOX's Dish Nation. In early 2018 she released a memoir with Brian Moylan, Pretty Mess, with color photos and personal stories. “I hope my intimate story can inspire readers to become their own strong, confident and vibrant pretty messes," she said in the book's press release. The book was ninth on The New York Times Best Seller list and fifth on the Publishers Weekly Bestseller List. In March 2018, she appeared in a Vogue feature and a short film after spending a day working for the fashion magazine. Her single "Cars" was released on April 10, 2018. The song interpolates the chorus of L'Trimm's famous single "Cars With the Boom" (1988). "Cars" received mostly favorable reception from music critics, who noted the song as significantly different from her previous releases. Despite the song's popularity among fans, "Cars" still did not manage to make an impact on the charts.
In May 2018, it was announced that she would reprise her role as real estate agent Farrah Dubose on The Young and the Restless for a two-episode guest stint. After media speculation, Girardi confirmed she is returning for the ninth season of The Real Housewives of Beverly Hills. Jessi Roti of Chicago Tribune wrote in late 2018 that "Jayne has become one of top reasons to tune in every week. Not just for the drama, but for the authenticity she added to the high gloss of the show with her fast-and-hard truths and keen self-awareness, and to catch a glimpse at what’s next for the performer, who was already established in the world of dance music." She hosted the Billboard Music Awards Red Carpet Live alongside AJ Gibson on May 20, 2018. The following August, she announced her collaboration with ShoeDazzle, an online shoe and accessories website. ShoeDazzle's commercial campaign features Jayne and her single "Xxpen$ive". She teamed up with ShoeDazzle as their latest “muse” and shared her 14 must-have favorite shoe styles for fall 2018. Customers will get to see her favorite shoe styles with a new collection each month. "I’ve been looking for the perfect partner to help me invite my fans to step into my closet, and my collaboration with ShoeDazzle affords my fans the chance to do just that," Jayne said in the press release. She also announced her plans to design her own line for the brand in 2019.
In September 2018, she was a featured speaker at TedxPasadena and gave a TED speech on transforming the future and putting words to action. Her speech was titled "My Unapologetic Alter Ego: Living Life as an Exaggerated Figment of People's Imaginations". She made a guest appearance on an episode of BET's sports drama television series Hit the Floor, in the episode "Hot Streak." She portrayed a media mogul called Beverly. In 2018, Erika Jayne appeared on various television shows to promote her music and book, including The View, The Wendy Williams Show, Larry King Now, Megyn Kelly Today, Steve and Kandi Koated Nights. In September 2018, she was as a guest editor for Fashion Week at E!. In late 2018, she produced a series of concerts at several venues, titled Erika Jayne Presents: The Pretty Mess Tour. The concert tour began on September 28 and ended on December 21, 2018. In October 2018, Jayne performed her single "Xxpen$ive" on The View in honor of her friend Meghan McCain's birthday. Michael Love Michael of Paper magazine wrote that Jayne was "wearing a sparkling leotard situation that we could just as easily picture on Britney Spears during her Piece of Me residency."
Fashion has also been a part of Jayne's music career and image. She has frequently worn clothes designed by Gucci, Moschino, Versace, Balmain, and Alexander McQueen. Tyler McCall of Fashionista.com called her "debatably the most stylish cast member of any Real Housewives franchise." In 2018, she was the first star of The Real Housewives media franchise to attend the CFDA Fashion Awards and was placed on several "best-dressed lists" after her appearance on the award show. Jayne wore a Tom Ford tuxedo with a Vera Wang dress shirt at the CFDA Fashion Awards. Her stylist Dani Michelle counts Jayne's outfit as one of her standouts. “I am not sure why it stays so close to my heart, but I think its because it was the perfect mix of strength, French fashion and unique Erika Jayne as one of the only women in suiting,” Michelle told Page Six. She has appeared on several magazine editorials, including Paper, Flaunt, V, People, Life & Style, CR Fashion Book and front covers of Billboard, Pasadena, CVLUX, Genlux, Celebrity Page. Jayne names Rita Hayworth and Marilyn Monroe as her style icons. She has also discussed how her mother and grandmother have been a continuing inspiration to her.
Girardi hosted the third annual "Run to Remember — Los Angeles" in honor of fallen police officers and first responders at The Grove on April 8, 2018. The event raised funds to serve families of those who have fallen, as well as supporting a variety of community programs such as police mentorships, education and scholarships for youth, equipment for local police and fire departments, at-risk-youth programs and veteran support. In October 2018, Girardi sold 16 different items from her wardrobe on eBay, including dresses seen on The Real Housewives of Beverly Hills, Billboard Music Awards and Grammy Awards. Ten percent of sales supported the LGBTQ charity GLAAD.