The 36-year-old man, arrested over Penelope Davis's killing, can be held until about 19:30 BST.
Mrs Davis, 47, known as Pennie, was tending to her horses when she was attacked.
Her body was found in a field on Leygreen Farm, Beaulieu by her husband, Pete on 2 September.  A total of five people have been arrested in the case.
Hampshire Constabulary said Mrs Davis, a supermarket worker, may have been followed from Sainsbury's in Hampton Lane, Blackfield.
Officers have appealed for witnesses who saw Mrs Davis's dark green Toyota Land Cruiser travelling between the supermarket and the field at Leygreen Farm between 13:30 and 15:00 on 2 September.
A 28-year-old woman from Hythe, Hampshire, arrested on Thursday on suspicion of conspiracy to commit murder, has been released on bail until 3 November.
Leanne Doyle, 24, of Beech Crescent, Hythe, was charged on Monday with assisting an offender and perverting the course of justice.
She has been bailed and is due to appear at Winchester Crown Court on 1 October.
A 22-year-old man, previously arrested on suspicion of murder, has been released on bail, while a 37-year-old man held on suspicion of assisting an offender was also bailed.
Crimestoppers has offered a Â£5,000 reward for information leading to the conviction of Mrs Davis's killer.

Seven Shi Tzu puppies and two full-grown lurchers were taken from the property in Glendevon Park, Winchburgh, between 07:30 and 18:00 on Wednesday.
The Shi Tzu puppies are tan and white in colour and are worth about Â£650 each. The lurchers have pale gold rough coats and are working dogs.
Police officers are appealing for witnesses to come forward.
Con Rachel Royan, of Police Scotland, said: "At eight weeks old the puppies are too young to have left their mother, who was not taken, and the owners are extremely concerned for their welfare.
"We would urge anyone who saw anything suspicious in or around Glendevon Park on Wednesday to please get in touch as we are keen to reunite them with their owners."

Network Rail is doing work in the Chipping Sodbury and Alderton tunnels and building a new platform at Bristol Parkway.
The improvements will run from Saturday until 15 September.
They will allow new trains to run on the Great Western Rail mainline, including new intercity express trains.
For the duration of the works, those travelling between south Wales and London should note:
For those travelling to and from south Wales during the August Bank Holiday weekend from 26 August to 28 August:
During the weekends from 23-24 September until 18-19 November, there will be further improvement work affecting south Wales and Bristol Parkway services.
Passengers are advised to check their journeys.
Police investigating the murder of a woman found dead in the New Forest have been given more time to question a man.
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Nine dogs including seven puppies have been stolen from a garden in West Lothian.
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Rail upgrade works affecting people travelling between south Wales, Bristol Parkway and London Paddington have begun.