ANSWER
Josie did not make a mistake
Step-by-step explanation
The vertex form of a quadratic equation is given in the form:
where (h, k) is the vertex
Jose rewrote the given equation to arrive at:
And her vertex was (2, -8)
Comparing this with the general form written above, we see that every step taken and the final answer are correct.
Therefore, Josie did not make a mistake.