u hammer away at her limbs until she drops down one of the peddals. it could be u have to go in and our of her range, but eventually she always drops a peddle down low enough to hit. u slice the arm continuously until it dies and she goes underground. you repeat this till she has no more arms and then finally you just wait for her to breath acid on u and u hit her head. u might be able to hit her head before the peddals are gone but i dont think so. its a long fight. but not really hard. just keep dodging and rolling.
I think I encountered a bug.. I managed to kill four of her petals, but she just won't lower the last one enough for me to hit it. She's just spitting acid at me all the time and her petal never gets low enough. Anyone with the same problem?