Ah, OK Louis, that was an appointment to submit the application. It was not an interview to support her application.
Those interviews are only undertaken by an Entry Clearance Officer at the British Embassy.
It would be highly unlikely that an interview would be needed.
If she indicated that she would prefer any needed interview to be conducted in English then it would be.
VFS are a private company working in a business releationship with The British Embassy to handle the front-end visa application submissions. They have absolutely no input or influence concerning the visa assessment or decision.
It's the waiting time now Louis.
I sincerely send all good luck and best wishes to you both for a speedy and positive outcome.