Queensland Police Ethical Standards Command is investigating the death of a 44-year-old Brisbane woman in the Ipswich watch house on Saturday, but prisoner advocate Debbie Kilroy says it is inappropriate for police to investigate themselves.

Police said in a statement on Sunday afternoon the dead woman, from the suburb of Ellen Grove, was arrested on Friday night on a warrant for failing to appear in court and for drug-related matters.

Debbie Kilroy, from prisoner advocacy group Sisters Inside, said the woman was Cindy Miller, a mother of two.

Police said she was being held pending a court appearance on Monday morning, but was found dead during a routine cell check in the early hours of Saturday morning.

Early indications suggest Ms Miller did not take her own life, the ABC understands.

"Cindy was loved by us all," Ms Kilroy said.

"No more information has been provided to the family. They're very distressed not knowing what happened.

"We were not aware of any health issues, so her death has come as a shock."

Police said the Crime and Corruption Commission would oversee the ethical standards investigation into Ms Miller's death.

Ms Kilroy said she would be contacting the coroner on Monday morning to ensure the CCTV from the watch house was contained, along with any documents relating to the woman's arrest and detention.

She said Sisters Inside was calling for an independent investigation.

"It's a big issue when police investigate themselves. This is not appropriate," she said.

"We are calling for an independent investigation, not police investigating police."