Penny Preston and the Raven’s Talisman by Armen Pogharian

When Shadow-monsters attack in the cafeteria, eighth-grader Penny Preston panics, starts a food fight and unknowingly creates a trans-dimensional rift. Summoned to the counselor’s office, she expects suspension, but instead discovers that she is misaligned and exists in more than three dimensions. Unless she immediately begins training to learn to handle her powerful abilities, she risks losing her sanity. She agrees to secretly train with her counselor and his friend Master Poe, an exile from the seventh dimension trapped in a raven’s body, to keep her home town, Piper Falls, safe from higher-dimensional beings seeking to gain god-like powers in our dimension.

Together with Simon, her telepathic multi-dimensional cat, Penny struggles to save her relationship with her best friend, protect her universe, and uncover her connection to Arthurian myth.