The boyfriend of Catherine Wells-Burr has been charged with conspiracy to murder her.
Rafal Nowak, 31, will appear before magistrates in Bristol on Wednesday, Avon and Somerset Police said. Nowak's former partner, Anna Julia Lagwinowicz, 32, has already appeared in court to face the same charge.
A police spokeswoman said: "Detectives investigating the murder of Catherine Wells-Burr have charged another person with conspiracy to murder. Rafal Nowak, aged 31, will appear at Bristol magistrates court. A 38-year-old man remains in police custody where he is being questioned."
Earlier on Tuesday, Lagwinowicz, a Polish national, made a brief appearance before magistrates charged with conspiring together with other persons to murder Miss Wells-Burr between May 1, 2012 and September 13, 2012.
The defendant, of South Street, Taunton, Somerset, was remanded in custody to appear before Bristol Crown Court on October 9.
Miss Wells-Burr's body was discovered by firefighters who had been alerted to the blazing five-door vehicle by passing motorists shortly before 6.30am off the A358 in Ashill on September 12.
Avon and Somerset Police have appealed for witnesses, describing the death as "tragic and brutal".
Miss Wells-Burr, known to friends as 'Caf', lived in Chard, Somerset, with her parents and sister Leanne.
After gaining a first-class degree in business management at Bath Spa University, she went to work as a business analyst for Chard-based Numatic International Ltd, known for Henry vacuum cleaners. Her parents have office posts at the firm where her boyfriend Mr Nowak, 31, also works.
Jayne and Phil Wells-Burr said their daughter was an "amazing, special person" who was excited about starting a new life with her boyfriend. "We have lost our beautiful Catherine; she was full of character, she was caring, loving, and had a bubbly personality," they said in a statement last week.