Okay,if you were older say 17-19 i'd say forget and forget but since your fifteen i say i dont care she is probally shy or a child enthusiast in disguiseafraid.Girls like talking so try asking her how she feels or listen to her.Girls are known to become very emoti(brown town) or extra angry for no reason .It's worked for me :)(except for the forget and forget, waiting to be 17:/ )
So pm if you thought this helped somewhat.
Brotherly,
Shadowed999