It may seem like semantics, but I think the point is important - I would feel like it was not that I wanted my mum to die, more that I didn't want her to live - and suffer - any more, which is an important difference.
I understand that the medical profession are bound to preserve life as long as possible, and that may seem cruel in circumstances like this, but there has to be a rule for everyone, to avoid someone having to draw a line where death is preferable, because everyone's situation is unique, and it's a slippery slope to go down, which is why the medical profession remain at the top of that slope, hard though that it for a lot of people, and their relatives, to bear.