Wow this really sounds like a drag. Is she able to pin point where the smell is coming from? You have checked all the water traps to make sure one has not dried out? The drying out of traps is more a sewer smell then a musty smell. My nose tells me you have water pooling somewhere in the house. Since your friend lives in Phoenix Az she probably does not nave a basement. It sounds like the professionals need to be brought in. You have had plenty of suggestions here. Please let us know what happens. I live in south Phoenix and I'm curious.