For me what worked first try and had me hardly take any damage was staying between her tails, turn as she turns to stay behind the whole time and using charged r2s (hunter axe) into the back half of her body seemed quite safe and the fight was over in a minute or two.
I know the head is the weak spot but sometimes dealing less damage in exchange for being in a safer spot and taking less damage is a good approach
Plus you can summon help near the entrance to the boss room if you want
Staying between her tails and moving with her to stay behind her the whole time worked for me to first try her. Just stay behind where it's safe and hardly take any damage, I know the head may be a weak spot but sometimes avoiding damage is (often) more important and staying behind her works great for that, I only used a couple vials the whole fight