Tensei Reijou wa Boukensha wo Kokorozasu

When young Serephione has a fateful encounter with Lou, the cute and fluffy guardian tiger, it opens the floodgates to a torrent of memories. She realizes she had a past life as an office worker in which she loved to read fantasy books, including one featuring the infamous villainess...Serephione Granzeus! After using her immense magical power in battle, the novel's Serephione was defeated and condemned to die alone. The surest way to escape that fate is avoiding magic school altogether...so Serephione vows to hide her magic and become an adventurer instead! But what will she do when major characters from the book threaten her plans?

(Source: J-Novel Club)