As others have mentioned above, Eikthyr, rested 20 or more, tasty mead and alternate stamina potions, and use the terrain for cover. Beat her last night for the first time, (2nd attempt), I had fully upgraded silver armour, and full upgrade draugr fang.

For food, I used serpent stew, eyescream and turnip stew. As for arrows, I had been saving needles and went through a stack of them and a stack of fire arrows, resulting in my bow being down to about 5-10% durability.

That was my 2nd attempt at taking on Moder, the first didn't end well, as a pack of wolves and a fenrir chased me down the mountain to my death, having got Moder down to around a 3rd of her health, so on the 2nd run, I drew Moder down the mountain to, in my case an area just above a swamp and plains border, which I had prepared a bit of terrain for, with some trenches for cover, which felt a bit cheesy tbh, but I did not want to deal with the locals as well as Moder if possible. Ran off to portal home, and then returned to fight her more on my terms.

On the first attempt, I was using up found poison arrows, saved from crypts, and obsidian, the damage seemed weaker, and my bow would have needed a repair or back up bow, had I not died.

Roro4066, I like the idea of melee, sounds horrific, I did have a go at hitting her with my silver hammer, but she hit back hard, so tail between my legs, I stuck with the bow. Next time I should try a different approach :)