Although the story was inspired by (and quotes in full) the Bob Dylansong, it reminds me more of "Puff the Magic Dragon", which also ends abruptly when a growing child abandons his/her animal friend(s).
The writing is awkward at best, even without the occasional Rouge Angles of Satin problems. However, to be fair, I've seen much worse.
My major complaint is with the story's premise. First, I have trouble believing that the pets' friendship would fall apart just because one of them (in this case, Penny) has to leave. Is the pets' relationship that weak, or was there something special about Penny that kept them together? The fic is so short, the author can't even begin to explain. (It doesn't help that we never learn what caused the shocking fight between Zoe and Pepper, which leaves Pepper with an Eye Scream injury.) And considering that the TV show is based on Blythe's special bond with the pets, and Blythe is such a kind and admirable person, I can't accept that she would ever abandon the pets, let alone do so as callously as she does here.
Also, I can understand someone wanting to add emotional depth to LPS; it's a silly (if enjoyable) series that could use more of it. However, going to the opposite extreme isn't the best way to accomplish this; the author takes the show way too seriously, burdening it with melodramatic baggage that it shouldn't have to carry. To me, this is an endemic problem with dark fics, especially the ones based on light, happy childrens' shows, even if the writer has the skill to pull it off (which usually isn't the case).
To sum up: If you want to read an LPS dark fic, this is a good place to start. But if you want to read this or any dark fic, then I have a question for you: Why?
Fanfic Not bad as Dark Fics go, but still a Dark Fic
If you're looking for a Dark Fic based on Littlest Pet Shop (2012)—a relatively high-minded one, not a Troll Fic that tries to shock you with sex and violence— then you'll probably enjoy HoldTheTruthForever's The Times They Are A-Changin' (2013). It's gotten good reviews at FanFiction.Net, and it's mentioned on the series' fanfic recommendations page, which is where I first heard of it. Me, I had some problems with it. Here are my observations:
To sum up: If you want to read an LPS dark fic, this is a good place to start. But if you want to read this or any dark fic, then I have a question for you: Why?