I have a cousin in America who wants to visit and have fun. I have my own house. Female 40 years old, but never married. Is it easy to refuse a visa?

You might as well not mention that you have cousins. Just sign up for an American tour. In the eyes of visa officers, cousins are weak. As an unmarried woman, the visa officer can't be suspicious.

It's good that you have collected enough information to prove that your family constraints are sufficient. The visa officer asks you what you want to do in the United States. You tell him that you are 40 years old, want to go out and have never been to the United States. Give him a detailed travel plan so that he won't be suspicious.