Cr Howlett said the council’s pursuit of her private emails because of a NSW Supreme Court fight with deputy mayor Paul Nichols – including some relating to her mother-in-law Margaret Howlett’s murder – was ‘‘the final straw that broke me’’ and a ‘‘fishing expedition’’.

‘‘This is a very grubby attempt to get into my private information, including information on my mother-in-law’s murder, and I’ll resign before they get it,’’ she said.

Margaret ‘‘Peggy’’ Howlett was brutally sexually assaulted and murdered in April, 1994. Her murder is described as an ‘‘on-going police cold case investigation’’.

Cr Howlett’s resignation will cost ratepayers $80,000 for a byelection, but will head off a likely second costly NSW Supreme Court challenge to Singleton Council code of conduct proceedings against one of its councillors.

The council was warned earlier this month that Cr Nichols’s challenge could cost ratepayers more than $200,000. The warning was issued as it launched separate code of conduct proceedings against Cr Howlett.

Cr Nichols was investigated for maintaining contact with two Carrowbrook brothers involved in a 13-year dispute with the council over a road through their property.

Cr Howlett is being investigated for media comments to the Newcastle Herald about the road dispute and requesting details from general manager Scott Greensill about the appointment of the assistant general manager.

Cr Howlett said she was bitterly disappointed by conflicting information Barbara Perry’s office issued to the Herald in February, relating to councillor complaints, and a letter from her department on Monday declining to investigate issues raised.