What is this little white thing that my chilean rose tarantula dropped?

If it looks like a spot of white-out, then it is the waste product which is initially liquid and then dries out. If it has a three dimensional shape and has texture it could be just a left over food bolus, which is what the spider makes if it does not eat all of its food. It is not likely to be an egg sac, it would be much larger and she would be very protective of it, by that I mean sitting or hovering over it.