Harry Potter and The Elven Girl

Lessica Everwood, a legendary elven deity and mercenary of the Frag Team, embarks on a high-level dungeon campaign designed for divine beings. Accompanied by her all-elemental fairy familiar, Elivina Pearl-Eli for short, she steps through the entrance, expecting a formidable challenge. Instead, an overwhelming darkness engulfs her.
The next thing she knows, a fierce wind howls around her, Eli's frantic voice urging her to wake up. Lessica's eyes snap open-only to find herself plummeting from the sky toward an unfamiliar landscape. The Dungeon's towering halls are gone.
Reacting instinctively, she casts Float just in time to slow her descent, landing in the middle of a vast lake. Walking across the water to shore, she quickly checks her Pip-Boy-only to discover that its advanced functions are locked, her connection to the Dungeon is severely restricted, and only select items in her vertical locker remain accessible.
A discarded newspaper provides her with a shocking revelation: she's on Earth-but not her Earth. Worse, she's in the United Kingdom-a location she instantly recognizes from a world she has only read about.
Realizing the need to blend in, Lessica changes out of her dungeon-run attire into something more appropriate. Using magic, she conceals her pointed ears and alters her eyes to appear more human. However, another unsettling truth emerges-her divine powers are locked, and she has been de-aged to 115 years old, leaving her in the equivalent of her elven teenage years.
Determined to find a way back home, she sets out with Eli (who remains invisible for safety). But before she can make sense of this world, she stumbles upon two boys being attacked by dark creatures. Acting on instinct, she draws her divine sword-one of the few items still accessible to her-and swiftly slays the monstrous threat.
Only after the battle does she realize the weight of her actions.
One of the boys she just saved is Harry Potter.