Honestly, the default recommendation is always Jane Austen or the Brontës, which is fine, but sometimes you want a protagonist who throws a punch, literally. For a contemporary fantasy twist, 'The Priory of the Orange Tree' by Samantha Shannon is an epic standalone with queens, dragonriders, and alchemists, all women who are driving the political and magical conflict. The narrative weight isn't on romance saving them; it's on their own choices and sacrifices.
If you prefer something grittier and more morally ambiguous, check out the 'Mistborn' trilogy. Vin's journey from a scared street urchin to a figure of immense power is a masterclass in character development where her strength is both a weapon and a psychological burden. It's not just about fighting; it's about learning to trust and lead when your instincts scream otherwise.
For a complete tonal shift, 'Circe' by Madeline Miller reimagines the nymph from the Odyssey as a formidable witch forging her own path through exile. Her strength is quiet, born of patience, profound loneliness, and a deep connection to her craft, which I found more affecting than a dozen battle scenes.