I usually don't read young adult books or fantasy, but I read and enjoyed yours. Yes, the plot is somewhat trite. The girl finds she is special. Usually she is a princess, not a fae, but the plot line is the same. She as a failed romance, goes to a special school, has wonderful friends and finally fulfills her promise. All well and good, and hard to make a fresh story. However, the variety of the far characters were charming, the cockney and London dialogue were interesting to this American, and the protagonist had a great character arc.
Read the story now
I thought the gargoyle having a valley girl speech pattern was, like, out of character for a gargoyle. But then, I have never talked to a gargoyle. Maybe they do talk, like, girls from northern Los Angeles.
There is some editing of misplaced sentence to be done, but nothing that bothered my read.
Your story flows and has many great elements. Perhaps you could finish it and provide a worthy challenge for your female version of Harry Potter. It will be quite engaging.