It's not usually compulsory, however, the whole year group is probably going out at once and if your DD doesn't organise something she may not have normal classes at school and have to sit in a year 9 class for the week. Work experience is also sometimes tied to a subject and may form part of the assessment for that subject (ie English - resumes and writing a diary and report on her placement. )

FWIW- I think if she can't get a journalism placement then she needs to sort a backup option. Many people don't get to work in their chosen or trained field and its a good "lesson" to understand that sometimes we don't get to do our chosen job or career.