Here's the thing with tough subjects: they need time to be processed. In a novella with 100 pages and a number of tough subjects, there's simply not enough space to handle them properly.
Happenstance offers several topics. Drugs, terrible home conditions, bullying to name some of them. We have Erin, bullied by two other Erins, all of them birthed on the same day, going to the same school. Our MC-Erin used to be friends with them until they began freezing her out, and the bullying started a couple of years before this novella takes place. With Erin struggling with her mom's drug abuse and her situation at school, I already knew here there wouldn't be space enough in this book to give this the proper care. There are so many things that are just touched upon, when they could've made and should make for a full length novel. To avoid spoilers, I won't spell out the plot twist around 60% or so, but this too got too little time. The explanations are loose, the reactions hushed by as is the resolution as well.
The real problem for me, however, is the characters. They're so stereotypical. Erin, bright girl coming from a terrible family, bullied, yet – according to our hero – amazing, and have always been. Short stories are always limited when it comes to character development, but there is nearly none here for any of the characters. They're all just stereotypes. Like our hero, Weston. Good guy, coming from an upstanding family, together with the most popular girl, great at sports, and is one of the popular guys in school. Yet, he's oddly genuine, kind, and so much more than he appears. Yes, and he's getting into Duke University on a scholarship, just like his dad wants. But Weston wants to do art, and his dad is completely ignorant of this. (Okay, I can't be the only one thinking about Chad Michael Murray's character in A Cinderella Story here, can I? Pretty much everyone is a character from this movie, to be honest.)
In conclusion this is nothing new, and doesn't bring much new to the table. Not with the shortness of the story and the already-seen characters. I'll admit to liking this better than Beautiful Disaster, but only because Weston wasn't an abusive love interest, even if Weston had his moments too.