A notorious murderer who is serving a life sentence at HMP Cornton Vale has pleaded guilty to attacking another inmate.

Sheriff William Gilchrist has expressed his frustration at having to deal with the case and has now requested a report from the prison's governor.

Nicolle Earley was jailed as a teenager for killing a grandmother during a row over £5 and a borrowed cigarette.

On Friday, she pleaded guilty by solicitor's letter at Stirling Sheriff Court to assaulting another inmate at Cornton Vale Prison near Stirling, where she is serving her sentence.

Earley assaulted fellow prisoner Melissa Sloan by repeatedly punching her on the head in the incident in the all-female jail.

Ms Sloan, 32, of Paisley, Renfrewshire, is understood to have been released since the attack, which occurred on November 14 last year.

Prosecutor Ruaraidh Ferguson said he could not provide the court with Earley's expected date of release or say when she might next be eligible to apply for parole.

Sheriff Gilchrist deferred sentence until March 16 for Earley to be brought to court. He also called for a report from the jail's governor.

He said: "I'm not sure what the court's supposed to do with someone who's serving a life sentence for murder, for punching another prisoner.

"What am I supposed to add to that? I don't see what I can add to it or what I could do that couldn't be done by the prison governor."

Earley, now 24, was just 16 when she kicked and stamped 63-year-old Ann Gray to death at her home in Crosshill, Fife, in 2008.

She was jailed for life in 2010 with a minimum term of 14 years for the murder of Mrs Gray, her grandmother's neighbour. Earley was a regular visitor to Mrs Gray's house.

Earley was given an additional year and a half sentence, to run consecutive to her current sentence, two and a half years ago after she sent letters covered in blood and scrawled with swastikas threatening to torture and kill a solicitor and a woman she had a grudge against.

Her trial at Edinburgh High Court was told that the day before the murder, Mrs Gray had apparently borrowed a cigarette from Earley on the understanding she would give the teenager two in return.

The following evening Earley went to collect them, along with £5 she claimed she was owed for shopping.

An argument followed, in which Earley knocked the pensioner to the ground before repeatedly kicking her and stamping on her.

Pathologists found Mrs Gray died of head injuries.