"The idea of playing with Rosie again after so many years was something I never imagined would be possible," said Balfour, who now plays with the Bath Philharmonia.
"I felt honoured to be doing this with her, to be her sound, her music, her violin and to have her next to me again was wonderful, really wonderful.
"I can remember the first day Rosie came in. She had the kind of musical look about her that gave us confidence in what she was doing. I am a rank and file but she was a solo player. She had everything ahead of her. After the accident I remember the orchestra felt broken."
To use the computer interface, Johnson focuses on coloured lights on a screen which allow her to select notes and phrases to be played and alter a composition as it is performed by live musicians. The intensity of her mental focus can even change the volume and speed of the piece.
Professor Eduardo Miranda, project leader from the University of Plymouth, said: "I had this thought, just imagine if it would be possible to read information from your brain to compose music. When I met Rosie there was something that clicked. I knew that she would understand."
Speaking of the moment when Johnson was first able to control the interface, Miranda added: "That moment was magical. It was a dream I had and a dream that seemed impossible. The system is reading Rosie's brainwaves. It took 20 years. It would not have been achieved if I had not had the chance to work with Rosie.
"We were all in tears. We could feel the joy coming from her at being able to make music."
This year Johnson will receive an MBE for services to music. The team is hoping that the technology will eventually provide many more patients with the ability to express their feelings even when they are unable to speak or move, through music.
A film of the concert has been created as part of Volvo's Human Made Stories series in collaboration with Sky Atlantic.