I feel horrible...

I got a b-day e-card from a girl I used to work with and am friends with but haven;t spoken to in a few months ....

She said Happy B-day...but then writes so how was the wedding? Can't wait to see pics from your honeymoon!

I thought she knew that we were getting marrried next JUly and I feel bad that she thinks that she wasn't invited which she of course is going to be invited.

So I e-mailed her back saying that we are getting married next year and that of course she is going to be invited.

But I just feel so bad

That was very nice of her. And you have no reason to feel bad! It was a simple mistake and you let her know that she'll be invited to the wedding next year.