A quick google search provided this

https://www.evrmemories.com/tsa-and-airline-requirements-for-urns-and-ashes/

Our family faced such a situation recently. After following all the guidelines and obtaining all paperwork, no one said one thing about the remains in the carryon. Similar to getting the health cert for your pet, they probably won’t ask, but you must be prepared just in case they do ask!
Best of luck to your friend.