girlfriend blackmailing a married man

After having relationship with a foreign lady, realised mistake and now she is blackmailing through social websites against a married man. Please advice on this what action she can take as she has lot of chat details and photos etc. My husband has confessed that he did a mistake but she is not ready to forgive him. My husband did not tell her that he is married but later on she discovered about his marriage. Is there any legal advice or precautions we can take look for?