The only way of triggering a normal fight with the Hag, is to offer your eye as payment for an attempt at removing the tadpole. This will lead to an encounter just as you walk down the ramp to where her cauldron is. Doing things any other way, will result in the Hag not reacting to your presence at the final fight.
If you end up in the actual fight and get the Hag to 10% she will negotiate for her life and offer you an ability point, in the form of a clump of hair, I'm guessing you are meant to eat this.. If you have made this deal with the Hag, you will be greeted with a "quest complete" placeholder pop-up, when exiting the lair using the teleporter. Here you can choose from 6 placeholder options. I'm guessing each, represent an ability score type. I have tried choosing all of them (save/load) none of them give any ability score. Sooo sad
Also here is a video of my inventory with two different Auntie Ethel's Hair objects.. Apparently they come in all shapes and sizes.
Video:
https://youtu.be/oEKIWjo7Tbg
