DEAR MISS MANNERS: I am in a regular walking group where I have become friends with about a third of the walkers. The rest I’m polite with but consider them acquaintances only. I host an annual party at my home for my friends. I send out private email invitations and don’t discuss the event during the walks. One of the walkers, a rather clingy person whom I consider only an acquaintance, told me she heard I was having a party, and invited herself.