A woman in her waiting period is still under her husband’s control and protection. And as such, it is not allowed for anyone to take her as spouse. If anyone marries her during that period, the marriage is void.
Sheikh Abdul-Haleem Mahmud says:
A divorced woman who is still in her waiting period is not permitted to marry another husband. If she employs tricks, however, and marries another during her waiting period, the marriage is unlawful. She is not permissible for the husband (during her period from an irrevocable divorce), nor is she legal for any other man apart from him, until she is completely divorced from him or he dies and she completes her waiting period. If these aforementioned conditions are not in place, then she is strictly prohibited for any other man other than her husband.
If the woman approaches a man by herself during Iddah, it is an act that is legally abhorred. It is not allowed for her to be with any man for any reason whatsoever other than her husband. As for what many think that a woman who offers herself to a man will justify the relationship and thus become legal, It is a wrong claim. It is in fact, a trick from those people to abuse the religion and belittle the personality and dignity of female folks.