Like what other said agencies will only handle your paperworks for you. It doesnt mean that she is free of work for the visa or free of not showing up in VFS. All of the information you need really is in this forum, she just got to browse and read the threads. Also, it is not 100% that her visa will be approved because she used an agency. Visas are assesed by its own merits not by how good the agency handles it. You will only waste money.
If she cant face VFS then she might find it hard to face 2 immigration officers on her way to Britain (PI and UK) which is more harder than just handling a visa. She might start practising now.