Depends how she wants to configure the business, she could start as a sole trader in which case she would need to register as self employed and pay the appropriate national insurance rate, or she could set up a a limited company which would need to be registered at companies house.
I would guess that initially it would be less aggravation to start as a sole trader, (it is easier to convert from sole trader to Ltd company at a later date than the other way round)
Either way, it would be a good idea to consult an accountant just to make sure all the options are properly explianed.
I am a bit surprised that she has managed to arrange insurance without declaring the status of the company to the insurer.
Hope that helps