My first reaction to the OP was that 35,000km was way too may to expect from a chain/cassette but the following postings clarified the situation a bit. A small, light woman riding in flat terrain may indeed not wear out a chain in that time.

One recommendation to the OP: learn to work on your own bike. You sound very dependent on the local bike shops for both advice and service. For someone who rides as much as you do, the minor investement in the special tools and service manuals would be a wise move.