How can I defeat Eorforwine?

I have now defeated her. My main strategy was pressure and opportunism.

I equipped a Spear as my weapon, to allow me to attack quicker and easier after dodging, so I didn't need to close as much distance.

I did pepper her with a few arrows, trying to hit the soft spot on her foot.

The key skill was the slow time when dodging, as this allows you to watch for her attack animation and then sidestep it and get a few hits in to deal damage. The advantage of this is that you are close to her, so she doesn't throw any poison gas bombs on you.

Being close up to her also means when she tries to drink her healing potion you can attack her to interrupt it.