I have DC doing school leaver L7 accountancy apprenticeships in GB. As you may be aware PwC's onshore support centre (Operate) is based in NI so your DD needs to think about and investigate whether she would be interested in the accountancy apprenticeship route (available with PwC and others in NI) or specifically PwC Operate apprenticeships which are geared to different aspects of compliance, tech, project and process support. The other Big 4 do have equivalents to Operate but not in NI (Deloitte Cardiff and EY Newcastle, for example).
PwC's career website is very good, so encourage your DD to read everything and watch all the videos; also sign up for alerts about online Operate Q&A sessions and in-person visits to the Belfast offices. These are more likely to be scheduled in the Autumn period (ie not now).
There are often also work experience weeks usually targeted at those current in first year of A levels, held online or in-person in the Spring or Summer; applications are usually made in the first term of sixth form/college. These are also good practice for applying (usually) in the autumn of Y13 for roles starting in Autumn of Y14.
Having existing general work experience is great. It helps DC understand strengths and motivations and shows prospective employers DC have a mature outlook and work ethic.
Do be aware that all entry level roles involve a fair degree of coping with repetitive tasks whilst maintaining accuracy, so your DD will need to work out if she has what it takes to motivate herself in that phase of her career.
Reviews on Rate My Apprenticeship are a useful source of info about what the experience is like for school leavers already on the various schemes. My DC say these reviews reflect their own experiences and they themselves have uploaded reviews.
Hope that helps.