Exercise exercise exercise. I know he is little, but it does help. We use a flirt pole with our little guy. It's amazing the workout he can get in ten minutes with it. It's awesome for when the weather is crummy too. It also gives a little mental stimulation, which a terrier definitely needs.
Here is the link
https://www.amazon.com/Squishy-Face-...70_&dpSrc=srch
I would also tell her not to worry too much about the noise in the apartment in the beginning, as long as it is during the day. She could also talk to her neighbors and explain what she is trying to do. Bring a plate of cookies
Now if she finds out that someone adjacent needs to sleep during the day, that would be something to consider. I guess my point is to be pro-active with the neighbors instead of waiting for them to complain.
How big is he? The neighbors may not even be able to hear much. Also, I would put him somewhere where he can't have access to the main door. Most noise travels through the entry doors.