your right, your'e only suppose to do the same type of job. but if its cash in hand, then there is probably only a small risk of her getting caught.
This page explains if you are allowed to do any other work outside your normal hours for which your work permit allows.
A person who has a work permit is able to undertake work, provided:
it is outside of their normal working hours;
it is no more than 20 hours a week;
it is in the same profession and at the same professional level for which the holder's work permit was issued; and
they are not employed by a recruitment agency, employment agency or similar business to provide personnel to a client (does not apply to Sports and Entertainments work permit holders).
The work permit holder is not allowed to enter self-employment, set up a business or join another business as a director or partner without obtaining further permission from us.
Under the following categories of the work permit arrangements, work permit holders are not permitted to take supplementary employment. These are:
Business and Commercial and Sports and Entertainments multiple entry work permit holders;
Training and Work Experience Scheme; and
General Agreement on Trade in Services.
http://www.ukba.homeoffice.gov.uk/wo...aryemployment/
