This reminds me of one of my first clients.
I had always written about Airplanes before (my passion and the thing I know about the most).
She wanted my help writing a script on the history of the US Dollar, for one of her youtube videos. I was frozen, but I decided to help her.
I did not know that my skill was to write, not to write about planes, and that sometimes ghostwriting is all about putting on a costume and pretending to be your client.
Once you learn that you can just write about anything, everything changes.