My friends being selfish....?

My friend she moved two hours away about a month ago. Now she's coming back on Saturday and our big group of friends are going to see a movie and then she's sleeping over. The problem is, is that my other friend she's like " i need some time with just me and her so i just want to have a sleepover me and her." It's not fair she's friends with all of us and we want to see her too. Ahhhhh.... so annoying don't know what to tell her to tell her it's not fair without being mean. So what should i say?