The Prophet (peace be upon him) warned us against committing that which is doubtful or dubious. By doing so, he said, we would be better enabled to safeguard our honor and religion.
If, on the other hand, we were to do that which is doubtful, we might end up doing what is forbidden.
Moreover, the Prophet also reminds us to shun activities that might inadvertently arouse suspicion in others.
Therefore, she is advised to refrain from such activities in the future.
If she is sincere in advising her friend's husband, she should do so through her friend. In other words, she should tell it to his wife and let her communicate it to him.
It behooves her as well as all of us to seek repentance to Allah consistently. Here is a Qur'anic du'a to repeat and meditate upon:
Allaahumma habbib ilayna al-eemaana wa zayyinhu fee quloobinaa wa karrih ilayna al-kufra wa al-fusooqa wa al-'isyaan
(O Allah, endear faith to our hearts and embellish our hearts with it, and make us abhor and detest disbelief, disobedience and transgression)