How should I tell someone I don't want them to come on vaca. ?

I have a friend who came on vacation with my family and I for the last two years. This school year an old friend came back and they became super close. That's fine and dandy except how we were all hanging out and then they just quit inviting me. I have way better friends than this and would rather them come with me. I'm not sure how I should tell her I would rather her not come, I haven't asked her to come; but she has automatically umed she is invited... :/