Under the mermaid angel Book

I think I read this when I was in 6th or 7th grade. I spent a lot of time in the library during those years and I came across this book. It was pretty deep to read this book at the time because I specifically remember Roxanne telling Jessie that she had a baby boy and it was Jessie's friend that always made fun of Roxanne behind her back. I also remember a girl who was called frog face because of how her face looked like from a car accident (mean). I also believe that Jesse was so much into science that she didn't believe the same things that Roxanne did. Also, Roxanne gave her fur coat to Jesse and she wore it all the time at school one day. I believe her gym teacher thought that Jesse wore it because she thought she was pregnant. I believe this story is called under the mermaid angel because Jesse went to a birthday party with Roxanne and there was a mermaid angel piñata (I could be wrong, I read this a long time ago). Towards the end, Jesse starts to believe in some things Roxanne believes in. Also, Roxanne's boyfriend she had a baby boy with, somehow died and he had a fake hand.