You might want to start by not thinking of it in terms of her "lacking mental capacity" and having a "lack of mental intellect" when it comes to the Borg, those are insulting and demeaning terms. A lot of very intelligent people were taken in by the Watchtower, what made them stay was the mind control used, not their lack of intelligence.
It's pretty common for people to say they believe things but then act in ways that are contrary to that belief. It's easy to skip meetings and do token field service, it's harder to actually admit you made a mistake and joined the wrong religion, that takes effort and a willingness to confront difficult issues and deal with emotional fallout from that. You will not get your wife to leave until she is mentally ready to do so.
If you want to help your wife, do not tell her anything, people do not like being told what to do. Instead try to draw her out and figure out what it is that keeps her clinging to a religion that she doesn't enjoy. Does she fear Armageddon? Does she enjoy the social aspects of the religion? Does she think other religions are corrupt? Once you figure out what she gets out of being a JW, then slowly start asking leading questions to get her to think.
Be patient, she made get there in time on her own, or you may help her out, but it may take some time.