Your daughter can work in a commercial kitchen as long as the employer notifies the local education authority and applies for a permit to be issued. The LEA will issue a permit as long as they are satisfied that the employment is 'appropriate' (e.g. in terms of safety) and that the usual conditions (e.g. relating to hours worked) are met.
While each LEA will treat every permit application individually, it's unlikely that there would be any problems granting a permit for a 16-year-old to work in food preparation. (Of course, entirely separate legislation requires that anyone working in food preparation must hold the relevant food hygiene certificate).
I note that your question refers to a 'week-end job'. It should be noted that, although your daughter may work for up to 8 hours on a Saturday, she is limited to just 2 hours on a Sunday.
http://www.direct.gov.uk/Parents/FamilyIssuesA ndTheLaw/ChildrensRights/ChildrensRightsArticl es/fs/en?CONTENT_ID=4002945&chk=AaZA0p
Chris