My wife occasionally sells copies of an original work of art

My wife occasionally sells copies of an original work of art - which we own - to the Canterbury Cathedral bookshop. This has involved setting up an arrangement with a local giclee printer who produce copies when needed. The order from Canterbury is erratic and depends on their sales. In an average year our net profit has been about £100.
In previous years my wife has submitted a tax return which has included this extra income. But this year - attempting to submit her form 'on line' - she has been bewildered by regulations and decided that she should enter the year's income from Canterbury under a new 'heading' and has attempted to register as a business. This has resulted in a plethora of forms and instructions which are bewildering. Attempts to phone 'gateway' have failed. Can you advise:
does an occasional activity - involving sums of less that £200 in a year - classify as a 'business'?
and if it does not, and only net income should be entered and taxed - how can she extricate herself and her tax returns from 'gateway'?
John Saunders