Am I wrong for feeling this way?

So 13 and my sister is a year younger and a close family friend just offered my sister and I to go overseas to America with them. My sister and I were so excited because ever since we were little we wanted to go there. When we told our Mum she said that she wanted us to go because it would be fun for us and she knows how much we ve always wanted to go but then she got really upset and was crying because she said she would rather us go with family and not friends. Now my sister won t go and I m not going without her but I don t understand why my mum is so upset and why this is so big to her. I feel like it s not a big deal and it s just a holiday with friends and now I feel guilty for feeling that way. And I feel selfish and I don t want to feel selfish. It s really confusing because and frustrating because I just don t understand. It s only a holiday to me, but for it s like I m getting married. She told me I deserve this but she wants me to make the right choice. I really really want to go but now if I went it wouldn t be as exciting.