How come some people look good with weight gain and some don't?

I have a friend that used to be skinny but now she is thick. A lot of people says she looks better now than when she was skinny. They said she is a woman with curves. I'm naturally thin. I was 99lbs but now I'm 124lbs. I'm still thin though and people say I look good. I'm 5'4 and 17. I'm glad I have curves but not as curvy is my friend. I mean she is THICK. If I gained weight I'll look horrible.