Really, I wouldn't worry about it. I'm sure that if it bothered her, than sometime over the last six years, she would have corected you. I let friends and family use the truncated version of my name, and take no offense to them addressing invites to Name, as opposed to Name-Name. I agree with another poster, if it is really bothering you, than quietly appologize at the anniversary party, and leave it at thet. Maybe tuck the info away for adressing future invites and cards.