You just have to take a deep breath and tell her. You don’t ever have to be disrespectful in telling her. The flip is that you don’t have to feel that by telling her means you are being disrespectful towards her.
Often times parents establish respect from the gate as they should. However when you become an adult you sometimes you go back to the child like mindset in thinking that speaking up means disrespect. It’s not true. Your house your rules. You have to know that in telling your mom she either has to accept that rule and still visit, she can get a hotel of her own and still visit or she can choose not to visit at all.
My hopes is she will visit regardless if she stays. I know plenty of others who have that as a rule and most times it’s understood. Smoking is a personal choice. Just because she’s your mom doesn’t mean her personal choice has to go over your rules. You’re an adult and being an adult means you have to be able to handle difficult situations. I know plenty of parents who taught that if you live in their house you play by their rules well the time has come to flip it to your mom honoring your rules in your home. And no it can’t be on the notion that her visit is only temporary so you can enforce the rules once she leaves. Even if a person who smokes outside will still bring the smell of smoke inside of the home. For a non smoker that smell can be too much. I know for me there is no smoking in our home nor around my kids.
I respect all who choose to smoke I just won’t even allow it around me and mine. Your mom is adult she can handle not smoking in your home. You just need to realize that you need to speak up without feeling like she is going to disown you for it. If she does it really reveals bigger issues that I’m sure you have been dealing with all along.