There is the "revolving door" JWs. Some use the system that way, for some it's instability in their head. Some want to be back with family, in that case it is somewhat understandable.
To disassociate is usually the individual's decision. Disfellowshipped is the JW judicial committee's decision. However, the organization now is twisting that in many cases and stating "so and so is no longer a JW," implying it that it was the former JWs decision. Individual's can often play the game for their personal advantage, but the JW organization is the one that manipulates more.
I thought I read before about 'a third' of disfellowshipped go back and get reinstated. Perhaps someone here can find a source in print.
This 'friend' was a conniver, a manipulator for his benefit. Sometimes, a male will want to get this girl they're interested in to marry, etc. with motive she'll will learn to be submissive to him now. As some JW men often like that teaching the most that they are "head of the house." Thus, he hopefully gains control.
I would only hope the non-JW girl can research about the WT organization. You seemed to know her enough to think she would not ever convert. Maybe she has a 'gut' feeling about it, however, she may need more than that, and need for actual knowledge and facts to reinforce her gut feeling. Can you suggest this site to her?