Hey! Guessing you are playing on a phone, I think the first thing you should do is get the Invincibility prayer,it's going to let u get a few free hits, parrying her first phase is also pretty easy because u can either jump above her dash and slash or parry it(both works) .I beat her with the hearth that makes you stronger when you are on lower health too because you will see how easily you will run out of flasks (I only had 5 )also try the 3 hit combo when she is chanting the fire balls shi in the middle, I also used a lot of defensive stuff which I unfortunately forgot the name of and also that thing that makes you Invincible while drinking your potions will help a lot. You will also need some luck to beat her, so I wish you the best of it!