How long is too long to send a thank you note?

TerriHugg

I'm kind of in the middle of this dilemma now in regards to my shower. I sent out all of my thank you notes the very next day of my shower. This was back in March. Just today I got one of the thank you cards as a "returned to sender." It was  a card I sent to my cousin who traveled out of state to be at the shower. Now I'm trying to figure out how to deal with the issue. Do I just promptly send the card back in the mail, do I call her to explain what happened? I just feel terrible because this girl is probably thinking I'm unappreciative of her travels and gift.