If you work on her system, you may also be breaking the law. Your ham license, although a valued document, is no substitute. You can help her contact the manufacturer of the stereo system. The Electronic Industries Association maintains a database of key contact people at each manufacturer. You may discover that the manufacturer already has some easy fixes available.
Some manufacturers even offer to do the work under warranty, or supply free filters.
Once you and Sally have located a manufacturer's representative to repair the stereo, you can help that representative understand the technical issues involved. The manufacturers are usually willing to assume their responsibilities fairly, but they do not always understand the fundamental causes of the problem, nor all the solutions. The ARRL has published The RFI Book . Buy a copy and read the chapters on fundamentals and curing audio equipment interference. You can also make your station available for testing when the electronic service person arrives.