This is a very normal scenario, one that all of us tax practitioners outside of the US hear several dozen times each week from every new client. Your client's first task will be put together a dossier of medical, school & work records since age of 2 to satisfy the SSA. You may already have discussed streamlined procedures, FBARs, PFICs, 8938s and so on with the client.
PS – Greeting from London, England. Grey and rainy ...