I have a question about letting someone down easy. (friends)?

okay. so. like we have friends. and we have to go on the trip to florida. and we can only have four people in a hotle room to share and stuffff. and likee, me & my bst friend wanna go together and this girl named jane too but like jane has this friend named betty too. and like we just found out like rachel has nobody to go with so we invited her to our group. but like ireally want jane to come iwht us. so like betty has nobody to go with now. but she doesnt know that. she thinks that me and my bst riend are going with her and jane. but like. we're trying to let her down easy and telll her that shes not in our group. HOW?