Girls weekend disappointment

About 6 weeks ago a group of 5 friends got together for a girls weekend and planned out next girls weekend which is in one and a half weeks. I have been in contact with all and just sent out an email reminder. One of the friends can't make it and suddenly has family from out of the country and a wedding the weekend of our event.

In addition, she has offered a different night for everyone to get together at her home some other time.

I know one of the other gals won't come now because they are close friends and she is recently introduced to us. So, anyway, I am unsure how to handle this. I feel somewhat upset but am unsure if it's selfish on my part or how to respond.