Nicole Richie has reportedly refused to visit her sick mother in hospital.The diminutive TV star is said to have fallen out with her adoptive mother Brenda, and has not visited her despite her recent hysterectomy. A source told the New York Post newspaper: "Brenda was in the hospital. She had a hysterectomy and Nicole hasn't visited her since. The two have not been getting along lately."According to reports, Nicole's rift with Brenda could be the cause of 'The Simple Life' star's recent personal problems.The 25-year-old has reportedly been seeing a therapist to try and combat her low weight. Nicole, who famously fell out with her best friend Paris Hilton before patching things up last year, has previously been treated for heroin addiction. Nicole was raised by singer Lionel Richie and his wife Brenda since she was a baby.The couple legally adopted Nicole when she was nine, but split soon after. Nicole's biological parents are reported to have been a drummer and backstage assistant who were working with Lionel at the time.