The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
I haven't seen many from Spain posting here, and although some of our folks may have fished Spain, you might do best locating some fly shops in Spain near Barcelona and asking them.
Also, a brief Google search turned up these ideas:
"Pyrenees : Wouldn't it be great if in the U.K. all you needed to do was pull up at a pub or restaurant close to a river, buy a permit and go fishing ? Well if you are fishing the Spanish Pyrenees this is exactly what you do! A fair grasp of the lingo is required, and you may face the odd knock back from locals protecting "their" fishing. But on the whole you will be given access to miles of crystal clear streams, full of wild Brown Trout." http://www.hartflyfishing.demon.co.uk/spain.html
See also: http://www.hola-andorra.com/fish/english/andfishi.html
Your girlfriend can probably track down additional sources for you--if you can ask her. Best of luck.