It's reasonable to want to know why she told such a lie, however, there are some cases in which people lie without a conscious thought to why they're doing so. It could be that your friend wanted attention or felt desperate to win (or keep) the interest of friends. These kinds of extreme attempts to win affection are embarrassing to admit to others, so a person who resorts to these measures is unlikely to open up to others about their motivations.

The bottom line is this: Your friend may tell you why she did it if you keep asking, or she may never give you a straight answer. That means you may have to "resolve" this for yourself.

How do you do that? It might help to ask yourself what's important to you in the situation. It sounds as though the main question is whether you can trust her to be truthful in the future.

If you think her lie is part of a larger pattern you see repeating over and over again, you may want to point it out to her and recommend that she talk to a school counselor or other mental health provider, if she won't talk to you. If she won't do anything about her behavior, then it might be time rethink the friendship; you may never be able to trust her.

On the other hand, if you think your friend was just going through a rough time during that period, and the lie was not part of an ongoing pattern, then you might want to give her another chance.

It's questionable whether her impulses will become "more self-destructive." Even the smartest and most "together" people have, at one time or another, done something senseless, but as they gain maturity, they find more effective and less alienating ways to deal with their emotions.

Whether she provides an answer or not, it's perfectly reasonable to let your friend know how her lie has affected your relationship. Maybe that would feel enough like a "resolution" to help you move on.

Take care.