She can always ask the vet the question: What would you do if it was your cat?

This is sooo hard....like almost everyone here, I have had to make the decision - he was not an old adult either, but his kidneys went to about 25%...he was losing weight and unhappy, he'd lash out if touched, but never hurt me.

I feel so for your friend...I am glad you are there with her.

HUGS to you both, and the dear kitty.