Hi. I'm new to the forum and am just having a browse through some of the threads. I read this one because I used to have a persian. He was a real special cat, and I miss him very much. His kidneys started to fail last June, finally quit altogether last September, and we had him euthanized. There were times that we had the matted hair problem. Partly he did not like being brushed. Since he was 4 1/2 years old when I got him, I can only imagine that whoever brushed him when he was young probably pulled too much and it hurt. I don't know. Anyway, brushing was a challenge.
What I want to say though is that maybe this client's persian is not being brushed properly. Either they aren't using the right tools or they aren't using the tools properly. When we would leave on holiday, a very good friend of ours would take care of all our pets. But every time we came back, the persian would be terribily matted. She says she brushed him every day, and I believe her. But I don't think she was doing it properly. The top of his coat would be fine, but the undercoat would be all lumps. He even picked up the nickname "Lumpy". Maybe you should have your client show you what brushes she uses and how she uses them. It might be that simple.