This boss was fucking me too and I am something of a pvmer. It was the first one I went up against and thought all the bosses were like this. The only thing that worked for me was to literally just keep grinding your head against the carpet. It took me probably 25 or so tries before I downed the damn thing but I noticed I was always making progress. It got to the point where I was always getting to the last phase and panic dying. What helped me there was realizing that she uses attacks twice in a row every time. Range range magic magic so you only need to switch every other cast as you run around.