Why does my sister have to be so mean?

Today I got dressed up since I don't really dress up during the week. So I recently cut my hair short. I used to have it long. Today I straightened it and it looked cute. I felt pretty. My sister has always seen me dressed up.. this isn't the first time. And it was awhile since she has seen me with short hair... so we got into this big fight (long story)……… and she just blurted out "you look ugly" and I felt bad afterward. I mean here I am feeling pretty. And then my sister had to say that.. I know she was problem joking. But still... she's way older than me too... I've been called ugly pretty much throughout my childhood. I mean I know im pretty. But even if someone jokes around and says im ugly. It hurts me. How can I not feel.. hurt when someone calls me ugly?..help. thanks.