Our first apartment in Switzerland was furnished too. We didnt live there for as long as you did, just almost two years but the handover standards were just as high, in fact higher because you simply have more things to clean. From the normal cleaning - which I hired professional cleaners to do, I washed the curtains (yup cheap Ikea ones), table cloths, bedsheets - everything. Gave all the surfaces and internal parts of the cupboards, wardrobes a wipedown as well.
Never again! You are best hiring professional cleaners with a handover guarantee. One of them will be present with you at the handover which will probably give the old dear a peace of mind that you hired the professionals to give her flat a proper wipe down, which will hopefully give you a psychological edge
Good luck with your handover.