I've noticed that in recent patches the Hag doesn't auto-flee after going invisible, especially if undamaged. She eventually flees when she gets to sub 30/20ish, but there's a good chance you can finish her off before she can make her escape.
I tend to forget about her until I finish the Underdark, so her fight tends to be very easy in my playthroughs because my party is so geared up. Bursting her down in the hut is definitely the easiest way to go, and her invisibility is pretty counter-able by almost any AOE - IIRC even a Shatter spell can reveal her (I forget if it's because of concentration or the game is programmed differently from the TTRPG rules). She's relatively vulnerable to crowd control since her saves aren't actually that great.
However, in my experience, while bursting her down on the top floor is the easiest, it does not provide the best rewards. To get the stat boost, you need her to surrender, and only the version* of her in the lair does that. Furthermore, at least in Patch 6, you can get different awards depending on what you do once she surrenders (probably a bug)
- If you intimidate her into giving you extra powers AND let Mayrina go, you get only the +1 STR consumable.
- If you let her HAVE Maryina after beating her, you get the +1 STR consumable, and also a quest award pops-up that lets you choose another +1 of any stat).
So while it's more difficult to go through her lair and fight the lair version of her (who has more tricks), right now in the EA you can get 2 more stats out of it. I also really like that rest is restricted now in your lair - really creates a sense of urgency (although I'm not sure what happens if you backtrack and go rest) and challenge.
* Side Note - due to a weird graphical bug, I have noticed that the game actually spawns a brand new Auntie-Ethels once she's escape to the lair. I.e. the Ethel you fight in the hut is not the same in the one in lair. I'm going to try to play around with it next time to see if I can duplicate items or get her to spawn and kill the one on the main floor(i.e. maybe non-lethal damage would do that).
