Using her power to create a way to escape from the prospect of her loss feels like an interesting concept to me.
The being actually has a part of the person's soul, so she isn't exactly a substitute.
Where to draw the line would actually make it harder for the protagonist to let her go, since as long there's magic power available, she doesn't really HAVE to.
Her costumers situation is totally different, that's precisely why that works for them, having just one day forces the people to make the most of that time.
Having just read Yuria's point of view is great, along with the protagonist resolve to not repeat tragedy, i'm certainly enjoying the story right now.