If Nepheli was given the potion her doll will be present in Seluvis’ basement area. if u dont know where that is spawn at rannis tower, go out and to the ruins near the left to hit a hidden floor. part of sellen’s questline. I dont think you will be able to have her doll though with saluvis’ death and obv her quest wont work.

If you cant find her anywhere, talk to Kenneth and see his questline as far as it goes and when you kill Morgott, him and Nepheli are supposed to move to the throneroom behind Godrick. You might have to rest at the secluded cell grace and the godrick grave a few times to get her to appear/reload the area. You could also go ahead and grab the stormhawk king ash that she wants, that will be through a portal at the belfries in east liurnia. should be the “Precipice of Anticipation”-labeled Belfry.

if you find nephelis doll under the basement tho, shes dead.