A friend of mine is has an appointment as research staff without any postgraduate degree, let alone a PhD. However, she has years of research experience and has single-handedly reviewed impact factor 8 journals due to her extreme specialization. I told her she cannot claim any experience as her boss may have delegated it from his own refereeing work. She is looking for jobs in academia/industry. Can she claim to have reviewed for these journals on her resume/CV?
If she has reviewed for these journals, then she has, regardless of who asked her to do it, and she can certainly put it on her CV (it's accurate and she can back it up).
One caveat would be if she wrote the reviews but they were submitted under her boss's name (with the journals' agreement) - in that case, it would be important for her to make clear that she was doing the reviews in lieu of her boss, and wasn't asked to do them in her own right. In other words, she certainly has the reviewing experience, but was asked because of her boss's expertise in the field and not her own (even if she may have that expertise as well).