Wait...did...did your mother actually just say something that made sense? I am so confused.
But yeah, I've never received an offer letter for anything, and I work for super-big-crazy Redacted, Inc. So I think you're fine. Don't get me wrong, it's completely dumb that they can't assign a local-to-you drug testing company to your case, but it's not surprising given government red tape is a thing that exists.