For me, it depends on how much I care about her as a friend.  If I do not care very much, I would probably opt to avoid conflict and just avoid making any plans with her-- basically distance and end the friendship that way, without drama or conflict.   If she means more to me than that, the next time we made plans I would share with her that I although I have forgiven her I have not forgotten the times I have been disappointed by her and that I need reliable friends (basically warn her that our friendship is on shaky ground and could be destroyed if she is not more conscientious than she has been.) 

I believe that you teach others how they can treat you-- if you allow them to treat you badly and do not make it clear that what they are doing is a problem, they will continue doing it.  I want to have friends who are basically conscientious and reliable.  If the person is too far from that, I either cut off or at least not rely on them much and try to make friends with healthier, more responsible people.