Secondary characters are important in any story. They need to be three-dimensional just as much as the main character does.
One of Isabel’s best friends is Skylar Linton – Sky for short. She’s feisty and opinionated, and she’s definitely got a gutsy side. Thing is, she also has a very large problem, and it doesn’t look like it’s going to go away. She won’t let anyone see how vulnerable she really feels inside.
No wonder she gets on so well with Isabel.
Sky is Isabel’s friend, but I really hope she doesn’t fall into the “best friend” stereotype. Hopefully she’ll be better fleshed out than that.
P.S. If you want a REALLY good example of a best friend who isn’t a “best friend”, take a look at Stiles Stilinski from Teen Wolf. He is amazing.