The 'Fashion Star' mentor -- who is expecting her second child with Eric Johnson, her fiance of two years -- even skipped her little sister Ashlee Simpson's birthday party for four-year-old son Bronx Wentz because she didn't want to be around Joe, reported Us magazine.
"One of her girlfriends says it's because she doesn't want to be anywhere near her dad," a source said.
Even with Jessica absent, "Bat for a Heart" singer Ashlee, 28, and her ex-husband, Fall Out Boy rocker Pete Wentz, 33, hosted a comic-themed fete for their son at the Coop in LA's Studio City.
Jessica's fellow 'Fashion Star' mentor Nicole Richie, 31, and her firstborn, Harlow, 4, also attended.
"The kids put on costumes and took pictures in a photo booth. It was sweet!," said a source.
Jessica, meanwhile, is gearing up for the arrival of her second baby. "Jessica loves being a mom. She is really overjoyed," said an insider.