Asking for a friend social security

it is the creation of an account under either of the id systems now being used that my friend will have the most difficulty with.

That's what the good civil servants who work at the U.S. Embassy in Mexico City are for. I found them extremely helpful, albeit under a different federal administration that was still designed to help We The People. Here's the website they need to get started from.
https://mx.usembassy.gov/federal-benefits-unit/