Northumberland

Thanks you for all the helpful suggestions.

She'll be there for about a week, staying in a city centre hotel - I may join her, not sure yet. She may want to hire a car.

Alnwick castle and gardens, Seahouses, Farne Islands and of course Hadrian's wall. Bamburgh for the castle and beach.
Newcastle has lots of good restaurants and plenty to see and do.

How long will she be in Newcastle? The S.O. has a flat in Bamburgh so we know the area extremely well. Will she have a car?

ps AmazonUK have a book by Brian Long, 1967, for £5 second hand which I think is the one I had.
And tell your friend to be careful if she ventures out "on the Toon" in the evening - it's very lively !

Northumberland is my home county, though don't live there at the moment.
I would think an American would be interested in ancient history, so the Roman Wall would come first - Corbridge to start.
The coast is beautiful if you have fine weather - suggest Bamburgh, and maybe Holy Island.
Northumberland is famous for its old castles - suggest you buy a book about The Castles of Northumberland - I used to have one, but it's disappeared .
Good luck!