Another thing you need to keep an eye on is, if boss raise hand before disappear, that means she'll appear near you with quick slash attack, if you're drinking HP potion, you'll get hit.
This will keep few times, but sometimes it will only once, then other kind of attack.
When boss drop about 1/3 HP, she'll appear at middle, and make wall shorter. Also, you can't hit her this time.
Can cause damage when she fall down after she make wall shorter.
Then, if you see boss raise tail, that mean next time she appear will be 3 times swing attack + front 5 spread shooting.
If you see this, get right or left, then you'll not get hit. BTW, this can block.
Normaly, boss will appear next you, like screenshot, she appear right after me, this time you can attack boss as more as you can, but still need to keep an eye on boss's action, normaly, boss's action are random, so it might just appear, or different kind of attack.