What do you mean she took the oath not intentionally
? If she did not want to take the oath she should have said I don't want to take an oath. Was someone holding a gun to her head if she didn't? If she swore by Allah to do something or not to do something then this is either a "yameen" or a "qassam". These things are serious. She should consult a local imam or scholar to clarify the rulings of this and discuss the matter in detail.
And are you a male friend or a female friend of hers?? The best advice I can give her right now is to stop talking to the person who she swore that she would stop talking to. That's the honourable thing to do.