Barbara Doggett appears in flashbacks in John Doe (season 9) and in the final solving of her son's murder (in Release, season 9). Though it is unclear when she and John Doggett divorced but she has been his ex-wife for quite some time by "Release."
She comes in for line-ups when John Doggett finds some suspects during his new investigation triggered by looking into mobster Nicholas Regali. She seems to have accepted the death of her son better than John Doggett did.
Her and John poured the ashes of Luke John Doggett into the ocean when Doggett finally found the killer, Nicholas Regali.