Sister Freide, how do i kill when under-leveled?

Unkindled i have like 700 or so HP. I want to kill her so i can beat the game using her weapon, since im doing a scythe run. I have 9 estus +3, and i dont have the titanite to get anything above +4. I want to cheese her to death and just finish her off for that awesome weapon, which i'm set on getting, but how? Carthus Curved Sword Bleed? Backstab spam? Poison? Idk. Maybe all? How do i do it? This is my first run in a year so it's tough. I've also been using the NPC. And my friend when he can play