I dont know for sure so you need to check into it. I don't think that you will need a CRB simply because she is only coming into your salon for a few days and there will be several people about. The school will have vetted you beforehand to determine that your place of work is suitable environment. TBH if it was that you needed to be CRB checked then all staff members would have to be CRB checked and thats just a nightmare situation for those doing the checks, think of all the places students have work experience all over the UK.
CRB's are mainly for people who are going to come in contact with vulnerable people and its for one organisation only. For example, I am going to be a mentor working with people with mental health problems. Thats 1 CRB check. I am also going to be working within a school as a teacher/mentor thats a 2nd CRB check. I am also going to be teaching older people IT skills and thats a 3rd CRB check. So I have to fill out the form 3 times.
The best advice I can give you is contact the school and if you have any concerns always have at least 2 adults with her at all times. Hope this helps.
anne xx