Selecting a PLB strikes me as something that should involve the person who will be carrying it. This is a pretty personal sort of thing. He'll need to know why it's a good idea to have one, he'll need to get into a habit of carrying one, and he'll need to know when to use it, etc.
In my experience, the biggest obstacle to overcome to get someone to carry a PLB is the cost. When you give it to them and ask them to carry because you are concerned about them, they almost always do. I generally recommend the ACR ResQLink, which is what I carry, unless weight it an absolute critical issue, then the Ocean Signal rescueME PLB1 will do.
If she wants tracking, etc, then the SPOT will work.