I rescued a large tegu that is black and white.  Is there anyway to tell which tegu she is?

Yes . If it has beaded skin then it is an argentine. If it has smooth skin the it is a columbian. Also punch in google tegus and they should have pictures of the different localities

Argentine B&W's also have ~4 yellow dots one near each limb near where the beading meets the abdominal hide. Another thing to look for is on thier snout and Argy has 2 scales and the Columbian has one. Last hint is if it has tried to kill you it's probably a Columbian.