This fight is similar to the one with Le Rauxe, there are some differences. I do the following:
At the start, use pistol/magic to slow her down. DO NOT LET HER USE HER WHIP, cuz that will probably mean your death. Once you have slowed her, jump in front of her (i first tried to jump in her back, but she turns faster than me). Once you have landed, start using the sword right away - the goal is to not let her use the dagger. If she manages to make enough distance to use the whip, jump out of her range and repeat. There are 2 potions that heal 10 each, take advantage of them.