A 32-year-old has been charged with conspiracy to murder university graduate Catherine Wells-Burr, police said.
Anna Julia Laqwinowicz will appear before magistrates in Bristol on Tuesday.
Miss Wells-Burr's body was found inside her burning car last Wednesday morning in Ashill, near Ilminster, Somerset.
Two men have been arrested in connection with the investigation, Avon and Somerset Police said. The men, aged 31 and 38, remain in police custody where they are being questioned.
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 that passed the site of this crime 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."
The grim discovery was made by firefighters alerted to the blazing five-door vehicle by passing motorists shortly before 6.30am on Wednesday off the A358.
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.
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.