Traps seem disgusting, but they are humane and you can see the dead animal right away, unlike poison where they die in a corner somewhere and stink the place up.
I like the cat idea... if your friend likes and can have cats, nature's best rodent control! :-)
~B
P.S. Rat activity will increase with the cold weather. They go into garages and storage areas to get warmth... they aren't stupid! I was told by a pest control guy that they don't like change either. So if your friend rearranges the garage a little, it might deter them for a bit. Also if she can find the source they are coming in from and close it up, that would help. Rats chew EVERYTHING, so she needs to make sure that she uses some kind of metal to close up any areas she suspects they are coming through.