I am indebted to all of you for taking the time to reply with lots of good comments, information and arguments. What a mine field! I guess if you grow up in the system it seems the norm, but to an outsider it seems like the most complicated tax system in the world! Unfortunately for many, myself included, one doesn't pay sufficient attention to boring tax laws when falling in love with a foreigner!! Adopting a baby in the US and subsequently deciding to return to England, I never gave it one minutes thought that she would one day be subject to her country of births tax laws. Who knew!
It is, ultimately her decision and you're right, a very personnal one as to whether or not she thinks she may one day want to return to her country of birth. For the last 4 years she has probably made between £18000 and £20000 a year before UK tax, so I think that, according to information given here, will mean that she needs to file forms.
As far as the SSN goes, can someone just clarify that again for me. She was born in April 1988. I have no recollection of ever applying for a SSN, but like I said she was adopted, so someone else may have done it? Am I right in thinking that she quite possibly and legitimately may not have one due to when she was born? If she doesn't have a SSN, how can the US government track her and how does she even file tax forms without one?
Please don't take this the wrong way, but I have to say that I'm eternally grateful that she doesn't have to register for the Draft!
Once again, many thanks.