A 32-year-old woman is set to appear in court charged with conspiracy to murder university graduate Catherine Wells-Burr.
Anna Julia Laqwinowicz will face magistrates in Bristol after Miss Wells-Burr's body was found inside her burning car last Wednesday morning in Ashill, near Ilminster, Somerset.
Two men aged 31 and 38 have also been arrested as part of the investigation and they remain in police custody.
Detective Inspector Simon Crisp, who is leading the inquiry appealed for witnesses to come forward.
Firefighters were alerted to the blazing five-door vehicle by passing motorists shortly before 6.30am on Wednesday off the A358.
Avon and Somerset Police described the death of Miss Wells-Burr, who holds a first-class degree in business management from Bath Spa University, as "tragic and brutal".
Miss Wells-Burr, known to friends as "Caf", lived in Chard, Somerset, with her parents and sister Leanne.
Parents Jayne and Phil Wells-Burr described their daughter as 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. She had a wonderful sense of humour, and was an amazing, special person.
"Catherine had achieved so much in her short life and had worked so hard to gain her bachelor of honours in business management, gaining a 1st class degree from Bath Spa University. She was so happy starting her life with Rafal and excited about their future together."