Answer:
Yes.
Explanation:
Assuming that what she means by "gone" is "eaten", then she is indeed right.
4 pizzas sliced into 8 pieces is the same as:
4 x 8 which equals to 32. [4 x 8 = 32]
So, if all of the pizza was gone, then all or 32 of 32 (or 32/32) was eaten.
She is otherwise wrong if part of the pizza slices were thrown away unbeknownst to them.