"the" cult? Jesus himself is followed, so any of us who are religious are in a "cult". We're not in the "occult"; but I think, if you are interested in helping your friend -- and there is any trust between you, and not just a condescending relationship; there are only a couple of options. Cry, learn about the other religion so as to be able to enter into a meaningful dialog, find ways of respecting your friend even though her religion is changing, or just be frustrated.
If your friend is influenced by JW; it sounds to me like she is easily scared. JW's seem to capitalize on fear; fear of course, is the beginning of wisdom, but not its goal. We need to respect God in order to learn to love him.
I have a suggestion, though I will have to ask around to find out what issue of the "watchtower" magazine it was in; but JW's didn't always hold all the doctrines they have today. Probably one of the clearest examples is blood transfusion; I am pretty certain that I saw a watchtower magazine from say the 1940s to 60s or so which had an article approving of blood transfusion.
The issue with JW's is hard for me to understand, I've only had two or three even talk with me; ( I get blacklisted by mormons and JW's, and they stop coming to my house; I don't know why, they just don't answer my questions about their claims, even if I try really hard to be gentle.. ) But in any event, I do know that they practically swear by the Watchtower magazine as the Gospel truth; and although she didn't walk away from them immediately, one lady who was shown it did eventually leave them once she ordered her own copy from them directly (That's the best thing).
Unfortunately it was quite bitter to her, for they are an ostracizing community. Leaving them isn't as simple as having a change of heart -- entire families and friends disown them if they do.
I might suggest you consider doing a Google search on Blood Transfusion and JW's; because I am not sure I can find the issue number.
In just about every Christian denomination I have seen, there are mistakes in peoples beliefs; very rarely have I found a person who really took the time to try to understand the scriptures without being influenced by family, friends, and their own ignorance. All I am saying, is, be gentle. There is little that can be done to recover someone who says "I like pastor so and so, because he is soooo nice." -- only people open to listening and sharing can really be reached; so don't throw your pearls before "swine" you'll just become more miserable.