If she is planning on doing that while being an active JW, she will be counsel on the possibility of not doing that assuming she was not the one who committed a sin and that lead to divorce. If her husband was responsible biblically on the matter of divorce she is free to marry again but only in the lord. If she marries him again there won't be no ceremony at the hall, she will have to do it in private no JW's allowed. and will if she confesses what she did disfellowshipped for doing that.
Dating someone who is not an active witness although he was once your husband doesn't changes things, either he comes back and gets reinstated or forgets about marrying a witness.
you'll have to go deep in their situation however they can do w