It depends on your municipality. In some they have local ballots where every candidate has to be approved. If they are denied because of racist (or similar) reasons, they can appeal the decision to a court. I believe the cow-bell-lady did that, but i dont remember the outcome.

Edit: did some research, she was granted citizenship recently. Here is an article about her (in english): https://www.swissinfo.ch/eng/society/swiss-passport_dutch-troublemaker-finally-granted-swiss-citizenship/43143162