The guides shouldn't be outdated. I don't see much change compared to EA (except the loot you get from the hag). I do it this way:
Speak to the hag, mention her murder of Mayrina's brothers. Mayrina cancels the deal and Ethel sends her to her playhouse. Ethel vanishes, some fight them here, I never do but let her go. I kill the redcaps, easy-peasy with a lvl 4 group, then enter the playhouse through the fireplace. I kill the masks which can be a bit more difficult, you are possibly not at full power after the fight. Therefore I leave the playhouse and make a long rest. after reentry I jump thought the waterfall and climp down the ladders. If you jump beyond the first poison cloud and jump at the end, you only need to pass through one cloud. At the bottom I short rest, to get full hp.
Then I sneak towards the hag's position, visible by the red area. You should have Magic Missiles ready, at best another character has Burning Rays. It's important to have the ability to create rain (f.e. Cleric and/or Raindancer staff). It's nice to have flying minions in the group (Ranger or Warlock). I confront the hag, after the dialog the fight starts. She makes her copies and sets Mayrina's cage on fire. Hunt the copies down with minions and/or Magic Missiles, do damage to the real hag. Put out the fire on the cage with a rain spell (once I threw a water bottle and the cage fell down and killed Mayrina ...). When Ethel copies Mayrina, aim at the Mayrina wihich shows less hit chance.
BTW I always kill the hag and don't cooperate with her to get her hair.
You could perhaps also just shove the hag into the abyss, I did it one time in EA, you just lose the loot.
The Ethel fight was one of the two fights where I failed the first try in the EA, for me it always was an unpleasant affair. It was however extremely easy this time in the release (on balanced difficulty), I had no problems at all.
