The water spray is certainly an option, it won't hurt the pup and far better that than have people complaining to the council, does your friend take the pup to obedience classes? and the obvious one does she go out for lots of walks during the day so that she isn't bored, does she have lots of toys to occupy her etc etc. I have a dog who is 1/2 Fox Terrier and he used to be terrible, not with birds but Squirrels, my house backs on to a copse and farmland so there are hundreds of the little blighter's about, and he like your friends dog used to hurtle up the garden at 5am when hubby let the all out (have 4 dogs) and start barking like mad, but the hose pipe put paid to that (big garden) he was squirted with that 2-3 times and it did the trick, I'm not saying that he never barks at squirrels now, only that he associates barking at 5am equals water so he doesn't do it at that time any more, during the day if he starts, I have trained him to come to a dog whistle and that nips it in the bud before it gets too bad, all of the above together with good obedience training each day and exercise should do the trick.