The Girl in the Park by Mariah Fredericks
Not a bad teen mystery, though I wonder if they will figure out the murderer as quickly as I did.
Wendy is dead, found in the park. Rain knows that Wendy wasn't a good person all the time. She went after the girls who shunned her in a brutal way...by going after their boyfriends. But Wendy still deserves justice. Rain must overcome her embarrassment that comes with speech impediment to truly speak up for her friend.