Jessica, 38, who is desperate to perform a song by Ashlee's famed mother-in-law Diana Ross on the E! show, Ashlee + Evan, is disappointed her sister isn't making that happen, the source noted.
"Jessica's been enjoying life out of the limelight, but she's ready to test the waters on her sister's show," the insider said. "She's writing music and working on a song for the show's finale."
"Jessica wanted to sing one of Diana's iconic songs, but Ashlee refused to ask her. She thought it was insulting," the source noted.
Jessica is now raising two kids with her former football player husband, Eric Johnson.
She began her music career in 1999 with the album "Sweet Kisses," which sold 4 million copies.
Since then, Jessica has recorded six more albums. And, the insider said, if her performance on Ashlee's show is a hit, she's considering relaunching her music career.
But those close to the spacey blonde wonder if she can pull it off, according to the Radar source.
"Ashlee and Jessica's friends worry because Jessica is always a bit off and awkward, like she's in a daze," the insider revealed. "Ashlee is all for Jessica performing on her show. But she won't hesitate to cut Jessica off if she doesn't sing and look her best. "
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