What was the substantive offence?
He is in breach of the conditions but whether or not he will be the subject of a prosecution is another matter.
The American authorities have no jurisdiction. They can and will co-operate with the UK authorities but it is not all that likely that the UK authorities would seek to return him to the UK over this.
He would be breached in the UK but that is only really going to have practical effect if he is returned to the UK for recall.
She can always block him on social media sites or change email address etc. There are lots of things that can be done to provide immediate protection.
Can I clarify anything for you?
No, she won't be a minor much longer and that is an issue.
The reality is that if she wishes to have contact with him then that is something she is free to do in the long run.
It is quite unlikely the UK authorities will seek his return I'm afraid.
Apart from anything else, if she is 17 then she is over the age of consent for actual sex now.
The only reason there is potentially an offence here is that the age of consent for photography is higher.
But within a year she will be free to have contact with him as she wishes.
There is no means of seeking extradition on a private basis.
As I have said, the Americans have no jurisdiction.
There aren't really any means of forcing the police in the UK to do something they would not normally do.