Waste Pool T16 - help

Done low level waste pool map without issues, but seems to be T16 is something diffent.
On T16 map I manage to take 1/3 boss HP and after she started spam on me slow debuf and life degen. That debuff almost completely freeze me and I cant do anything about that. Curse immune flask not working there.

I manage to escape to portal once, but after I back, almost instantly got tons of slow debuff and almost could not move again till I die from life degen.

Lose all portal and still dont understand how to kill that boss in high level.
Please advice me :)

Turn the valve you used to start the boss fight to reset it's debuffs when they get too ugly.

https://pathofexile.fandom.com/wiki/Portentia,_the_Foul