Is this unfair for me to say?

My mother in law was offended and said it was strange we ask people to take off their shoes at the door. We have white carpeting as soon as people come in, so I don't think it was unreasonable. She came in anyway with her shoes on and left marks on our carpet. I told her she can't come over anymore if she can't obey that rule. Everyone else has no problem with it, and we have a basket for shoes and a bench right by our door for people to sit down and remove their shoes. Is that unfair of me to say?