Is it permissible to wipe polished surfaces that have been touched by a wet hand after using a washing-machine-laundered towel whose purity is doubtful?

The whispers (waswas) have reached a significant level with you. Therefore, we advise you to ignore these whispers, turn away from them, and pay no attention to them. You may adopt the Maliki school of thought, which holds that water does not become impure (najis) unless its characteristics change. Impurity is not determined by mere doubt. Abandon these whispers and use whatever you wish from your belongings without needing to wash or wipe them, even if your sister touches them with her wet hand; because the default principle is the absence of impurity.