And I am surprised no one has mentioned the problems with getting littermates - once the dogs reach maturity isn't there usually a problem with dog on dog aggression? I have an acquaintance who is currently dealing with this and one of her dogs will have to be re-homed.
If you're advising her about training in general, tell her about the necessity of separating the dogs often- one dog should go to class or on a walk or a training session while the other is left home. Frequently. They need to learn to be individuals, not treated as a pair all the time.
As to the fence- if you can't convince her to see reason, maybe you could try running through the training protocol you use when putting in an invisible fence? namely, you walk the dog on a leash up to the boundary and encourage the dog to back away from the boundary and give lots of treats and praise for doing so? For a rare few dogs that's sufficient to keep them in.