My sister and I are VERY close. We are close in age and do everything together and have for the most part the same friend group. We made a new friend recently and have hung out with her many times before together. Today, I was with that friend and she invited me over to spend the night. I just assumed she meant my sister and I both. All my other friends have always invited both my sister and I. I haven't told my sister about it and she was excited, but then later I found out our friend only wanted me over and not my sister..I haven't said anything to my sister yet. I'm not sure what to do because I don't want to hurt my sisters feelings, but I don't want my friend to feel obligated to have my sister over too. Any ideas at what to do?