This is All Your Fault, Cassie Parker
Fiona and Cassie are supposed to be best friends forever. No one else listens or makes Fiona laugh like Cassie, and that meant everything when Fiona’s parents were divorcing. They love each other in spite of their (many) differences, and even though Cassie cares a little too much about being popular, Fiona can’t imagine life without her.
Until Fiona’s diary is stolen by the most popular girls at school, and her most secret thoughts are read out loud on the bus. Even worse: Cassie was there, and she didn’t do anything to stop it. Now, for some reason, she’s ignoring Fiona. Suddenly the whole world has shifted.
While there are a few students who want to write, there are a lot of books that have such characters. I'd rather characters who are interested in a sport, or recycling, or helping at a pet shelter. The prevalence of phones and social media, and the effects that these have on middle graders, are realistically portrayed.
Fiona was an annoying character, but I enjoyed the friend and family drama. It's nice that you could read this or Drive Me Crazy first since the books are companion volumes and not sequels.