How Do I Word An Email To Where It Sounds Polite?

I met this mom who joined my playgroup site at a local bookstore. She had a negative vibe to her (I can feel people's energy since I'm kinda intuitive). She also was blunt and showed no expression on her face when I spoke. However, I was polite, smiled often, and supportive to her when she spoke, maybe that's why she liked me and asked me to come for lunch at her house this Sunday. How do I word my email to where I don't think it's going to work for us? I can not find a way to make the email sound polite.