Is the woman who reported another woman, whom she thought had relieved herself in the Haram, considered mistaken or a transgressor, after the reported woman swore that she had not done so?

Mere suspicion does not permit accusing others unless there is a valid indication and an apparent reason. Any suspicion for which there is no known valid indication or apparent reason is forbidden and must be avoided. However, if there is something that points to the accusation or a suspicious demeanor, then suspicion is permissible, especially if the matter relates to a legitimate interest, such as the defilement of a mosque with impurity. But if the suspicion is based merely on doubt, then one must seek forgiveness and repent, and seek absolution from the woman if possible, or supplicate for her in her absence.