Hi guest
Your sister really needs to learn howto train her dog, because if he is "trained" by someone else he still will not understand what rules are appropriate to his own home and life.
Find a trainer who uses motivational methods try
APBT and go along to classes (watch first to see if you like the trainer and methods) with the Westie.
Get your sister to read some good dog books too - not so much about training, but about understanding the dog, such as "Why Does my Dog?" by John Fisher from crosskeysbooks.com
Leigh Note: Go into 'edit' and have a look at the link Lindsay ;-)