Am I wrong?

Something has been bugging me for awhile, I haven't blogged about it because I think I am being silly. Sis please don't take this wrong. I just need to get it out there. My sister has a friend, it is her best friend. She calls my Dad Dad. It bothers me. I'm not sure why but it makes me sad. I wonder sometimes if it is because I fel like I am being replaced since I wasn't around for so long. I mean it is a point of honor for someone not your child to call you mom or dad. Why does this bother me so much? Am I a horrible person? I mean I heard her say it several times when I was visiting in Texas and I just let it go but the other day Sis told me she had called Dad for his birthday and her friend talked to him. Dad said now I have talked to all my girls. That really hurt my feelings but I feel bad that it bothers me. I don't know what is wrong with me lately.