Fortunatly I have never had to say or think that about any of my children.
But I have had other family members, that were so hopelessly ill, that it would be a blessing if they would pass.
I wish you would not have to feel this way about your child.
Feeling guilty about it is very natural, because she is your child and you don't want her to suffer.
I wish you all the best and strength to deal with this difficult time.