US Citizen Stuck In Australia (Running into dead ends about SSN)

EDIT: ⟟ just want to say, THANK YOU to everyone who commented and gave as much info as they could to help my friend in her endeavors back to the US, there were SO many comments so quickly that is was difficult to keep up with haha. We got a ton of great info that we are going to work with to get her here, and on behalf of Sloth, her fiance, and myself, we greatly appreciate all of you for everything, and wish you well in life!!

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Hi there, I'm posting this for a dear friend of mine. For privacy purposes, obviously I won't be using her name, so I will call her Sloth for this (this is a nickname we use lovingly for my friend.)

Sloth was born in the United States, to be more specific she was born in Nevada. Her family moved to Australia when she was young, a toddler I believe, and did not apply for dual citizenship. Sloth's mother was..for lack of a better term, very controlling of her life because she is on the spectrum (extremely high functioning autistic. like, so high functioning that I had no idea until she told me) so her mother never let her do anything (i.e get an id/license or a job) Fast forward years, her and her mother had a nasty falling out when she was 22 or 23 y/o, so she moved out. (she is currently 29)

Her mother had all of her legal documents, and apparently lost them years ago, but never said anything. After jumping through countless hoops, she got her birth certificate and has her expired passport. She has been desperately trying to move back to the US since she was 18 (when she tried to take control of her own life and things began to sour with her mother), but can't since she doesn't have her social security card, and she never knew the number since her mother never gave it to her, and even her mother doesn't know the number.

I have tried on my end (im in the US) to get information from the Nevada SSA, but ran into a dead end with that, and she contacted the SSA Embassy on her end and they sent her an email saying she needs to provide sufficient proof of her identity to get a replacement card.

So. How the hell is she supposed to prove who she is, when all she has is an expired passport and her birth certificate?