FMIL gave me her family's list of invitees several months ago. A few weeks ago she gave me the addresses to go along with those names. Between the two lists she must have realized she had misspelled one of FI's cousin's last name (she was recently married). I did not notice this change (it was one letter different) because I checked names against the original list when I made sure I didn't miss anyone. And mailed the invites a couple days ago. I noticed it when we got a gift from her in the mail yesterday. I feel horrible and I certainly don't want her to think we didn't care enough to get her name right. My question is when I send her a thank you note do I include an apology or just spell it right this time and leave it alone? I spent so much time making sure all the addresses and everything were right that it is making me sick that someone might think we don't care about them.