The Excel recruitment consists of a group interview, where you will be told about the company and asked to talk about yourself in front of everyone for around five minutes. Then you are given basic maths and general knowledge exams.
The second stage (if you pass the exams) is 1 to 1. They will ask you various questions about customer service situations, why you want to work specifically for excel etc. and also give you the opportunity to ask questions.
Good luck to your girlfriend, excel is a friendly company to work for with some interesting work at the moment.