Well it seems to me that there are two possiblities as to why she has decided to do this. One: She is lying when she says nothing is wrong or Two: She really cares about you and possibly thinks you could be the one. If it is the latter then she probably just wants to date other people to make sure that you are the one for her. Sometimes before people really decide to commit, they need reassurance that the feelings they are feeling towards someone are true, that they can not feel these strong feelings toward anyone else.
It seems to me that if she wants to date others the only thing you can do is let her go and hope that if you two are meant to be together she will come back after a short period of time. I am sorry I could not be of more help.