DiDA is the Diploma in Digital Applications. If your daughter has achieved the full diploma, rather than just the award (AiDA) or certificate (CiDA) level, it's equivalent to 4 GCSEs. Further information is here:
http://dida.edexcel.org.uk/home/aboutdida/
However, even though her qualification might be equivalent to 4 GCSEs, it's not equivalent to any specific subjects. Rightly or wrongly, I very much doubt that many City employers will want to offer her a position without GCSE Maths and English (at A to C level). It might be necessary for your daughter to return to college to attain these qualifications. At the same time, she could study additional options such as Business Studies and/or Keyboard Proficiency.
I'm sorry if that sounds rather negative but there's a lot of competition for jobs in the City (in all sectors). When employers look through an apllicant's qualifications, the first imaginary boxes they want to tick in their minds are usually the ones for Maths and English.
Chris