I tried planters on master mode several times, with the best gear and potions I could possibly get my hands on, and failed every time. This changed when I realized I was playing too scared. First stage goes as normal, circle around her fast with the flamethrower, and basically take zero hits, but once she goes into second stage, everything falls apart. I realized that her second stage practically locks to your up and down position, but is slower at moving side to side. So build an arena that is longer than taller. When you need to run the opposite direction because you ran out of space, drop a few levels, then immediately fly over her to the other side, and WALK to stay away from her with minimal dodges. I took the fight slower, and it went so smooth I was also embarrassed at myself for how bad I was doing before hand.