I am helping an elderly woman publish a book of her poetry. I am willing to pay the costs of the initial printing and to do the setup of the document under my own account (as a gift), but I would like any royalties to go to her.
Is there a way to do this, or must she have her own KDP account?
Payments go to the publisher, who as you describe it would be you.
She would need her own KDP account to be paid directly.
Alternately, you could receive the money in your account and then give it to her. You'll need to do 1099 forms, so that she would have the tax liability, and you could avoid said tax liability. However, because pretty much no one sells poetry books, it might just be a couple bucks of extra tax that you'd have to pay, so it might not even be worth it for you.
There are, by the way, no "costs" for printing a book through KDP or, the vastly preferable alternative, CreateSpace. CS is an Amazon company. I highly recommend going to CS and setting up the book there, using their Guided process where they talk you through setting things up (they also have phone support, which KDP-print does not have). If you do the book through CS, you can order as many copies as you like as "author copies," where all you pay is actual printing cost and shipping. No one gets royalties on author copies, but royalties were never going to be much of an issue anyway.
(Because it's print-on-demand, you can order say 5 copies to begin, then if there are more relatives to give copies to, order 5 more, or 12 more, or whatever you like. Avoid the basement-full-of-boxes trap.)
It's very generous of you to help someone reach the goal of seeing their work in print, even if it never sells to a stranger.