A woman is due to appear in court this morning charged with conspiracy to murder over the death of Catherine Wells-Burr.
Anna Julia Laqwinowicz, 32, will appear before Bristol Magistrates Court today.
Avon and Somerset Police said a 31-year-old man and a 38-year-old man have also been arrested in connection with the investigation, and remain in police custody where they are being questioned.
The body of Miss Wells-Burr, a Bath Spa University graduate who worked as a business analyst at Numatic International in Chard, was discovered inside a burning car in a field just off the A358 at Ashill, near Ilminster, last Wednesday morning.
Detective Inspector Simon Crisp, who is leading the inquiry, said: "I am still extremely keen to speak to a number of people who have not yet come forward.
"We know that there were many motorists who passed the site on Wednesday morning, and those people may have information that could help us.
"I would ask that you come forward and speak with us no matter how small you think your information may be, please let us decide.
"It is also important that we speak with anyone who may have been in the area between 3am and 6am on Wednesday, using the roads between Chard and Ashill (the A358).
"Did you see a red Ford Focus, five-door hatch back that may have been in company with another vehicle? If you did, please contact us."
Anyone with information is asked to call police on 101, or via Crimestoppers on 0800 555 111.