Answer:
What is missing from her experimental design is a control group.
Step-by-step explanation:
Every scientific design nowadays need a control group. This control group will serve as a comparison to her after she treats the other group with her hypothesis. In this case, the control group needs to be related to her hypothesis, so it would be a control group treated with the old chemical treatment. With this, after she treats the mouse she can do the comparison and the math needed to finish her research.